New Perspectives on Tropical Rain Forest Vegetation Ecology in West Africa: Typology, Gradients and Disturbance Regime Renaat Van Rompaey* IDS Bulletin Vol 33 No 1 2002 31 1 Introduction The ecology of tropical forests in Africa has been dealt with in a number of standard works (e.g. Aubréville 1938; Dawkins 1958; Richards 1964). Since these works many ecological studies have taken place in all parts of the tropics, and these have changed and nuanced many of the insights of these earlier studies (e.g. Hall and Swaine 1981; Whitmore 1975; Hawthorne 1996). In recent times, many global change studies have again added much further information about these ecosystems at other scale levels, including through the use of predictive modelling (e.g. Maley 1996; Alcamo et al. 1998; Jolly et al. 1998; Elenga et al. 2000). Some of the new perspectives forwarded in these more recent generations of ecological study are highly relevant both for understanding the ongoing interactions between people and forests in West Africa, and for the development of conservation policies in rain forest areas. In this article I will highlight three topics that are crucial to understanding change in the forests of West Africa. In each case, it becomes important to differentiate more finely than has often been done in the past between the kinds of forest where different dynamics occur. First I will deal with terminology, as much confusion surrounds the terms used for vegetation types and biomes in West Africa. In particular, it is important to compare terms between French and English, the two languages that, since colonial times, have dominated science and administration in the region. After defining the forest zone and reading from satellite imagery the extent of current forest cover, I will demonstrate the important variation in species composition that exists among currently forested areas, mainly related to the climate gradient. I will then expand on the dynamics of these forests and how well adapted some of their tree species are to severe disturbance, be it of climatic or anthropogenic origin. The article argues that the highly dynamic semi- deciduous forests recover well from it, in contrast to the evergreen forests, which are rich in rare and endemic species and much more vulnerable to disturbance.
Transcript
NewPerspectiveson TropicalRain ForestVegetationEcology inWest AfricaTypology Gradientsand DisturbanceRegimeRenaat Van Rom paey
IDS Bulletin Vol 33 No 1 2002
31
1 IntroductionThe ecology of tropical forests in Africa has beendealt with in a number of standard works (egAubreacuteville 1938 Dawkins 1958 Richards 1964)Since these works many ecological studies havetaken place in all parts of the tropics and thesehave changed and nuanced many of the insights ofthese earlier studies (eg Hall and Swaine 1981Whitmore 1975 Hawthorne 1996) In recenttimes many global change studies have againadded much further information about theseecosystems at other scale levels including throughthe use of predictive modelling (eg Maley 1996Alcamo et al 1998 Jolly et al 1998 Elenga et al2000)
Some of the new perspectives forwarded in thesemore recent generations of ecological study arehighly relevant both for understanding the ongoinginteractions between people and forests in WestAfrica and for the development of conservationpolicies in rain forest areas In this article I willhighlight three topics that are crucial tounderstanding change in the forests of West AfricaIn each case it becomes important to differentiatemore finely than has often been done in the pastbetween the kinds of forest where differentdynamics occur
First I will deal with terminology as muchconfusion surrounds the terms used for vegetationtypes and biomes in West Africa In particular it isimportant to compare terms between French andEnglish the two languages that since colonialtimes have dominated science and administrationin the region After defining the forest zone andreading from satellite imagery the extent of currentforest cover I will demonstrate the importantvariation in species composition that exists amongcurrently forested areas mainly related to theclimate gradient I will then expand on thedynamics of these forests and how well adaptedsome of their tree species are to severe disturbancebe it of climatic or anthropogenic origin Thearticle argues that the highly dynamic semi-deciduous forests recover well from it in contrastto the evergreen forests which are rich in rare andendemic species and much more vulnerable todisturbance
2 Advances in vegetationtypology and terminologyWhen studying the vegetation of West Africa onecomes across significant differences betweenFrench and English terminology for vegetationtypes Direct translation between these frequentlyleads to confusion Terms such as rain forest highforest moist forest dry forest woodland shrubland and savanna have different definitions inFrench and English A term like savane guineacuteenne(Guillaumet and Adjanohoun 1971) correspondsto lsquoSudanian transition woodlandrsquo in Englishliterature (White 1983) and to forecirct claire in theFrench translation of it (White 1986 Frenchversion) In French forecirct classeacutee is also used todesignate a gazetted reserve or domaine vacante etsans maicirctre reacuteserveacute pour lrsquoEtat (lsquoan empty domainwithout master reserved for the statersquo Parren1994) in Burkina Faso for example with veryshrubby vegetation (Gueacutehi 1993)
Following White (1983) I distinguish the lsquoforestzonersquo as existing where tropical rain forest can growas continuous vegetation cover On NOAA(National Oceanic amp Atmospheric Administration)satellite images taken in the dry season (February)one can distinguish this zone from the lsquosavannarsquozone north of it even if the forests are replaced byfallow vegetation (see Figure 1) because the impactof fire is different in each zone
North of the forest zone lies a more openvegetation belt often referred to as lsquosavannarsquoWhite (1983) concluded that the term savanna hadbeen defined in so many different ways that hecould no longer use it for precise classificationThus he uses terms such as woodland bushlandscrubland and (secondary wooded) grassland Onbetter soils these areas have at times been coveredwith lsquodrier types of peripheral semi-evergreen rainforestrsquo as an ecotone (or transitional zone) betweenforest and woodland It seems preferable to namethis biome after the woodland vegetation that it hassometimes carried than after the savanna which isfrequently found there under current climatic andland use conditions
French terms for these vegetation types are moreelastic There is forecircts denses segraveches forecircts claires (forwoodland) and formations herbeuses boiseacutees forwooded grassland (White 1983) In conclusion
the French term forecirct is used for vegetation typesthat extend much further north than does thevegetation that the English call lsquoforestrsquo The Foodand Agriculture Organisation (FAO) definition offorest ie land with more than 10 per cent treecrown cover of trees more than 5 metres high (FAO2001) seems to follow the French lsquoforecirctrsquo but is inno accordance to what Oxfordian botanists likeWhite and AETFAT (Association pour lrsquoEtudeTaxonomique de la Flore drsquoAfrique Tropicale) andUNESCO term lsquoforestrsquo This leads to very confusingstatistics eg Cocircte drsquoIvoire has about 7 million haof forest according to FAO definitions but only 2million ha of high forest as British terminologywould define it while 13 million ha of forest aresaid to exist in Mali (FAO 2001) In consequenceFAOrsquos figures concerning deforestation relate in noway to changes in rain forest cover
Figure 1 shows the forest zone as mapped by White(1983 black line) and as based on NOAA satelliteimages (Olesen 1994 light grey) The forest cover in1992 based on the same images (Olesen 1994) isshown in dark grey It is worth noting in particularthe difference between the two forest zoneboundaries in Sierra Leone White restricted the zoneto the existing continuous forest cover and thus justcovered the Gola forests of the extreme south-east ofthe country In contrast in the interpretation of theNOAA satellite image the entire southern half ofSierra Leone is classified as forest zone fallow Coastalsavannas in Liberia are also more restricted accordingto the satellite imagery than as mapped by White Ineastern Cocircte drsquoIvoire and Togo White included areaswithin the Guineo-Congolian forest domain wherethe satellite can no longer detect any forest fallowSouthern Benin is classified as part of the forest zoneso the so-called lsquoDahomey gaprsquo of savanna there(according to earlier analyses) appears in reality moreas a lsquosouth-east Ghana-Togo gaprsquo Not allclassifications of satellite imagery whether usingNOAA or SPOT (Satellite Pour lrsquoObservation de laTerre) vegetation 1 km-resolution show the forestzone as clearly as Olesen (1994) nor in the sameplaces Some precaution is therefore needed beforeusing such images to alter definitively how theboundaries of the Guineo-Congolian forest domainand its Upper Guinean epicentre are drawn
In Ghana the current forest area corresponds wellwith the actual forest reserves and national parks
32
Hawthorne and Abu-Juam (1995) assessed thecondition of all 214 Ghanaian forest reserves withregard to farming logging and fire impact Sixcondition classes were defined ranging fromlsquoexcellentrsquo to lsquono significant forest leftrsquo (althoughwhether these areas carried forest cover at the timeof their reservation is debatable see Fairhead andLeach 1998) Except for the least forested classessatellite imagery could not detect the differences incondition so for sustainable forest and protectedarea management this important information has tobe collected lsquoon the groundrsquo
3 The gradual nature of changesin species compositionAlthough vegetation maps may suggest that so-called lsquoclimaxrsquo forest types are uniform over theirrange the reality is much more complexFurthermore forest cover maps produced fromsatellite images (as in Figure 1) represent presentforest cover in a uniform colour while followingRichards (1964) some people talk about lsquothetropical rain forestrsquo After Oldeman (1990)however I prefer always to use the plural formlsquotropical rain forestsrsquo in recognition of the hugevariation and many exceptions that exist in what isone of the most complex ecosystems in the worldBotanical studies (Hall and Swaine 1981 VanRompaey 1993) now show that species compositionchanges continuously and gradually both locally inthe landscape and regionally along climaticgradients Most of the species in West Africarsquos rain
forests respond strongly to water availability orinversely to drought stress (Bongers et al 1999)although climate interacts with other factors such assoil type Thus badly distributed rainfall may resultin drier forest types or savanna such as occurs inparts of north-west Liberia through to Conakry onthe coast of the Republic of Guinea Howeverparent soil material such as the schists of easternCocircte drsquoIvoire give clayey soils that allow wetterforest types to survive even when rainfall is lessabundant In the south of Taiuml National Park in CocirctedrsquoIvoire Van Rompaey (1993) found semi-deciduous forests on granite bedrock with manyboulders at the surface similar to the forests foundin the north of the Park on gneissic bedrock Somekilometres eastward across the geological fault trulyevergreen forests existed on schist parent materialSuch mosaic patterns exist at the meso-scale inmany parts of the Upper Guinea region
Figure 2 shows a new regional forest gradient mapfor West Africa (Van Rompaey 2001) preparedusing national timber inventory data (more than 3million measured trees) This was processed in astandardised way using ordination techniques andspatially represented using a GeographicalInformation System (GIS)
In central Cocircte drsquoIvoire a V-shaped incursion ofwoodland and grassland exists within the forestzone called the V-Baouleacute after the people livingthere East of the V-Baouleacute the majority of theforests are of the drier semi-deciduous type
33
Figure 1 West Africa Forest cover in 1992 and forest zone according to Whitersquos (1983) map of vegetationand NOAA satellite imagery (Olesen 1994)
Renaat
Geplaatste afbeelding
whereas west of the V-Baouleacute this type becomesrare In coastal Liberia vast tracts of very humidevergreen forest exist of a type that is absent evenfrom Ghana and that is found only in south-eastNigeria and west Cameroon the Biafran forests richin Caesalpinioideae tree species
Hall and Swaine (1981) Hawthorne (1995) andrecent studies by the ECOSYN project (Universitiesof Wageningen Cocody-Abidjan Oxford) haveshown that these wetter forest types have higherspecies diversity are richer in rare and endemicspecies and can be considered as Pleistocenerefugia ie areas where forest species survived thecolder and drier spells in the Quaternary past
4 From the lsquovirgin forest conceptrsquoto lsquoperpetuity of disturbancersquo andthe different response strategiesof species
There was a time when vegetation ecologists triedto distinguish between primary and late secondaryforests in West Africa At the moment the majordistinction is between unlogged and logged forestas traces of anthropogenic disturbance have beendiscovered in almost all African forest ecosystems(Schwartz 1992 Maley infra White 2001)
In fact in Ghana Hawthorne (1996) recognisedthat in semi-deciduous forests many canopy treespecies are light-demanding or pioneer incharacter suggesting that the forests haveexperienced a heavier disturbance regime than inwetter forests (Figure 3a) The disturbance in thiszone in the past has mainly been climatic Over thelast million years this part of the forest zone hasexperienced a dramatic oscillation of dry and wetspells with dry phases being the most frequent (seeMaley infra) In this respect the semi-deciduousforest is a recently installed forest and this explainsthe abundance of pioneer and light-demandingspecies and the quasi-absence of rare and endemicspecies Hawthorne (1996) expressed this using aGenetic Heat Index corresponding to the averagerarity of the species in a forest (see Figure 3b)Anthropogenic disturbance from farming treefelling and road construction for example areexperienced by the tree species as the forest climategets drier At the same time forest fires burn litteron the forest floor which can improve conditionsfor seed germination and seedling installationwhile fires sometimes induce mast fruiting of trees
The regeneration strategy of these light-demandingspecies is one of discontinuous waves of highlysuccessful seedlings Thus they frequently lack thesmooth exponential size class distribution which
34
Figure 2 Forest vegetation gradient map based on species composition of timber trees from nationalinventories (Van Rompaey 2001) Forest reserves and national parks are shown in white or black outline
Renaat
Geplaatste afbeelding
35
Figure 3(a) Positive correlation between percentage of species with a pioneer character (Pioneer index)and the position of the forest in question along the wet-dry gradient (Hall and Swaine 1981 axis 1 score)in Ghana (Hawthorne 1996)
Figure 3(b) Negative correlation between average rarity of the species (Genetic Heat Index) and positionof the forest on the wet-dry gradient The very dry forests contain very few species so the index values aremore scattered
Renaat
Geplaatste afbeelding
older analytics in forest ecology would haveexpected comprising very many seedlings manysaplings and fewer larger trees This makes theirregeneration difficult to predict and theirsustainable forest management hard to model Forexample one can compare the pioneer timber treesMilicia regia and excelsa (Figure 4) mainly found indrier forests with the shade-bearing tree Tarrietiautilis synonymous with Heritiera utilis (Figure 4)from the wet forests The light-demandingness ofspecies like Heritiera shifts from shade-bearing inyouth to growing in full light when mature Miliciatrees were always found growing in sunlitconditions in the Ghana timber inventoryregardless of age (Hawthorne 1995)
The light-demandingness of a species can also beread from the form of the size class distributionsteeply exponential for shade-bearers to flatlyexponential or irregular for pioneers (Figure 4)Tarrietia and Milicia have equal densities among thebig trees of the respectively wet and dry forestswhere they occur but in the small size class in wetevergreen forests Tarrietia is very abundant Miliciasaplings (5ndash30 cm diameter) and young trees(30ndash60 cm diameter) are ten times rarer in dry semi-deciduous forest and moreover they grow in sunlitplaces which are often more difficult to walkthrough These densities seem to be sufficient forboth species to survive in the forests where they livealthough Alder (1990) was unable to model a stablepopulation from the mortality and growth data from
Ghana that he processed An explanation may bethat successful regeneration only occurs within atime frame of several decades which is beyond themeasuring period of the Ghana Forest Service
5 Conclusion no uniform rainforest zone but two clearlydifferent systemsThe rain forest zone is clearly not a uniform cover ofundisturbed forest Rather present-day speciescomposition reflects both past disturbance regimesand gradients of water availability as they interact witha complex of other factors including soil types andland use While the outcomes of these interactingfactors are highly variable over space and time it ispossible to identify two poles within the forest zone
l Forests with continuous water availabilitythanks to a fairly constant climate andor waterretaining soils evergreen forests rich in rare andendemic species because there has been littleneed for the species to migrate and fewextinction events
l Forests with a long history of climaticdisturbance with irregular water availability anda climate with irregular dry spells semi-deciduousforests with few rare species and little endemism
These distinctions have important implications forrain forest conservation and management The
36
Figure 4 Size class distribution of the pioneer trees Milicia spp in dry semi-deciduous forest and the shade-bearer Tarrietia utilis in wet evergreen forest (Ghana national timber inventory Hawthorne 1995)
evergreen forests are of the highest conservationpriority and by fortuitous chance also contain fewertimber species of high economic value The semi-deciduous forests are of lower conservation priorityfor the sake of rare and endangered species althoughthe currently-undisturbed form of these forests hasbecome very rare and thus merits protection at anumber of places These forests have many timberspecies of high economic value and are thus ofgreatest value from a timber productivity perspective
51 Implications for conservationpriority setting
From Figure 2 it appears that the protected areasand forest reserves within the Upper Guinea regionare spread over the vegetation gradient in a ratheruneven way For example
l Sapo National Park is the only representative ofthe very wet evergreen forests of Liberia
l The Nimba Reserves in southern GuineaLiberia and Cocircte drsquoIvoire are the only protectedupland evergreen forests
l Taiuml Azagny and Banco National Parks (CocirctedrsquoIvoire) and Nini-Suhien National Park(Ghana) contain wet and transitional foresttypes while Bia and Kakum National Parks inGhana are transitional forests
l Marahoueacute National Park contains the driestsemi-deciduous forest at its boundary towoodland and secondary grassland This typeis also found in forest patches in ComoeacuteNational Park in north-east Cocircte drsquoIvoire
This overview therefore suggests that if forestconservation strategies are to represent the regionrsquos
forest types accurately Liberia should give protectedarea status to more of its very wet forests especiallyin the high rainfall zone (4000 mm rain annually) ineastern Liberia extending some 100 km inland fromthe coast Equally more upland evergreen orsubmontane forests in Liberia Guinea Cocircte drsquoIvoire(eg the Monts de Dan) and Ghana (eg the Atewarange Hawthorne and Abu-Juam 1995) deserveprotected area status Furthermore the driest forestsespecially in Ghana where they contain several localendemics might be seen to merit more conservationattention especially where they are under threatfrom fire timber and firewood logging
In short recent perspectives and research invegetation ecology make forests in West Africaharder to classify and the classes harder to map thanwas thought before Many tree species show survivalstrategies that allow them to deal with heavydisturbance whether of climatic or anthropogenicorigin When deciding on conservation andsustainable management options for these forestsevergreen and semi-deciduous forests show highlycontrasted opportunities while both representvariable and dynamic ecosystems which challengeearlier management models based on ideas of stablepopulations and regeneration patterns
Notes I should like to thank Melissa Leach and James
Fairhead for inviting me to the inspiring Brightonworkshop My research in West Africa has beenfunded by Wageningen University (1987ndash1993) andthe European Commission DG Dev ECOSYNProject (1996ndash2000) Many GIS layers have beenprovided by Conservation International Washingtonand WCMC Cambridge I also thank MPE Parrenfor useful comments on the manuscript and WDHawthorne for many discussions about these topicsThe author can be contacted onRenaatVanRompaeyULBacbe
37
ReferencesAlcamo J Leemans R and Kreileman E 1998
lsquoGlobal change scenarios of the 21st centuryrsquoResults from the IMAGE 21 Model KidlingtonPergamon
Alder D 1990 Ghafosim a projection system fornatural forest growth and yield in Ghana OxfordManas Systems Ltd
Aubreacuteville A 1938 lsquoLa forecirct coloniale Les forecircts delrsquoAfrique occidentale franccedilaisersquo Annales de lrsquoAcadeacutemiedes sciences coloniales tome IX Soc drsquoeacuteditionsgeacuteographiques maritimes et coloniales ParislrsquoAcadeacutemie des Sciences
Bongers F Poorter L Van Rompaey RSAR andParren MPE 1999 lsquoDistribution of twelve moistforest canopy tree species in Liberia and Cocircte
drsquoIvoire response curves to a climatic gradientrsquoJournal of Vegetation Science Vol 10 371ndash82
Dawkins HC 1958 The Management of NaturalTropical High-forest with Special Reference to UgandaInstitute Paper No 34 Imperial Forestry InstituteUniversity of Oxford Oxford
Elenga H Peyron O Bonnefille R Jolly DCheddadi R Guiot J Andrieu V Bottema SBuchet G De Beaulieu J-L Hamilton ACMaley J Marchant R Perez-Obiol R Reille MRiollet G Scott L Straka H Taylor D VanCampo E Vincens A Laarif F Jonson H 2000lsquoPollen-based biome reconstruction for southernEurope and Africa 18000 yr BCrsquo Journal ofBiogeography Vol 27 621ndash34
Fairhead J and Leach M 1998 ReframingDeforestation global analyses and local realitiesstudies in West Africa London Routledge
Gueacutehi JI 1993 lsquoLa politique coloniale de protection dela nature en Cocircte drsquoIvoire (1900ndash1958)rsquo in JPouchepadass (ed) Colonisations et environnementBibliothegraveque drsquohistoire drsquooutre mer Nouvelle seacuterie Etudes13 Paris Soc fr drsquohistoire drsquooutre-mer 83ndash104
Guillaumet JL and Adjanohoun E 1971 lsquoLaveacutegeacutetation de la Cocircte drsquoIvoire Dans Le milieunaturel de la Cocircte drsquoIvoirersquo Meacutemoires ORSTOM No50 156ndash263
Hall JB and Swaine MD 1981 lsquoDistribution andecology of vascular plants in a tropical rain forestforest vegetation in Ghanarsquo Geobotany 1 TheHague Dr W Junk Publishers
Hawthorne W and Abu-Juam M 1995 ForestProtection in Ghana Gland IUCN
Hawthorne WD 1995 lsquoEcological profiles of theforest trees of Ghanarsquo Tropical Forests papers No 26Oxford Forestry Institute
Hawthorne WD 1996 lsquoHoles and the sums of partsin Ghanaian forest regeneration scale andsustainable usersquo Proceedings of the Royal SocietyEdinburgh Vol 104B 75ndash176
Jolly D Prentice C Bonnefille R Ballouche ABengo M Brenac P Buchet G Burney D CazetJ-P Cheddadi R Edorh T Elenga HElmoutaki S Guiot J Laarif F Lamb H LezineA-M Maley J Mbenza M Peyron O Reille MReynaud-Farrera I Riollet G Ritchie C RocheE Scott L Ssemmanda I Straka H Umer HVan Campo E Vilimumbalo S Vincens AWaller M 1998 lsquoBiome reconstruction from
pollen and plant macrofossil data for Africa and theArabian peninsula at 0 and 6000 yearsrsquo Journal ofBiogeography Vol 25 1007ndash27
Maley J 1996 lsquoThe African rain forest ndash maincharacteristics of changes in vegetation and climatefrom the Upper Cretaceous to the QuaternaryrsquoProceedings of the Royal Society Edinburgh Vol 104B31ndash73
Oldeman RAA 1990 Forests Elements of SilvologyHeidelberg Springer Verlag
Olesen HH 1994 lsquoTropical forest inventory usingAVHRR-HRPT and LAC data in West Africarsquo FinalReport on Contract No 5088-92-11 ED ISP CHGeneva UNEP-GRID
Parren MPE 1994 lsquoFrench and British colonialforest policies past and present implications forCocircte drsquoIvoire and Ghanarsquo Working Papers in AfricanStudies No 188 Boston African Studies CenterBoston University
Richards PW 1964 The Tropical Rain Forest Anecological study Cambridge Cambridge UniversityPress
Schwartz D 1992 lsquoAssegravechement climatique vers3000 BP et expansion Bantu en Afrique centraleatlantique quelques reacuteflexionsrsquo Bulletin de la SocieteGeacuteologique de France Vol 163 No 3 353ndash61
Van Rompaey RSAR 1993 lsquoForest gradients inWest Africa A spatial gradient analysisrsquo Doctoralthesis Department of Forestry AgriculturalUniversity Wageningen
Van Rompaey RSAR 2001 lsquoMegatransects inUpper Guinea how forest inventory data can beprocessed into a gradient maprsquo in Robbrechts Eand Degreef J (eds) Proceedings XVIth AETFATConference August 2000 Meise Belgium
White F 1983 lsquoThe vegetation of Africa a descriptivememoir to accompany the UNESCOAETFATUNSO vegetation map of Africarsquo Natural ResourcesResearch Paris UNESCO Vol XX
White F 1986 lsquoLa veacutegeacutetation de lrsquoAfrique meacutemoiresaccompagnant la carte de veacutegeacutetation de lrsquoAfriquersquo(UNESCOAETFATUNSO) ORSTOMUNESCORecherches sur les ressources naturelles Vol XX
White LJT 2001 lsquoForest-savanna dynamics and theorigins of lsquoMarantaceae Forestrsquo in central Gabonrsquo inB Weber LJT White A Vedder and L Naughton(eds) African Rain Forest Ecology and ConservationYale Yale University Press
Whitmore TC 1975 Tropical Rain Forests of the FarEast Oxford Clarendon Press
38
2 Advances in vegetationtypology and terminologyWhen studying the vegetation of West Africa onecomes across significant differences betweenFrench and English terminology for vegetationtypes Direct translation between these frequentlyleads to confusion Terms such as rain forest highforest moist forest dry forest woodland shrubland and savanna have different definitions inFrench and English A term like savane guineacuteenne(Guillaumet and Adjanohoun 1971) correspondsto lsquoSudanian transition woodlandrsquo in Englishliterature (White 1983) and to forecirct claire in theFrench translation of it (White 1986 Frenchversion) In French forecirct classeacutee is also used todesignate a gazetted reserve or domaine vacante etsans maicirctre reacuteserveacute pour lrsquoEtat (lsquoan empty domainwithout master reserved for the statersquo Parren1994) in Burkina Faso for example with veryshrubby vegetation (Gueacutehi 1993)
Following White (1983) I distinguish the lsquoforestzonersquo as existing where tropical rain forest can growas continuous vegetation cover On NOAA(National Oceanic amp Atmospheric Administration)satellite images taken in the dry season (February)one can distinguish this zone from the lsquosavannarsquozone north of it even if the forests are replaced byfallow vegetation (see Figure 1) because the impactof fire is different in each zone
North of the forest zone lies a more openvegetation belt often referred to as lsquosavannarsquoWhite (1983) concluded that the term savanna hadbeen defined in so many different ways that hecould no longer use it for precise classificationThus he uses terms such as woodland bushlandscrubland and (secondary wooded) grassland Onbetter soils these areas have at times been coveredwith lsquodrier types of peripheral semi-evergreen rainforestrsquo as an ecotone (or transitional zone) betweenforest and woodland It seems preferable to namethis biome after the woodland vegetation that it hassometimes carried than after the savanna which isfrequently found there under current climatic andland use conditions
French terms for these vegetation types are moreelastic There is forecircts denses segraveches forecircts claires (forwoodland) and formations herbeuses boiseacutees forwooded grassland (White 1983) In conclusion
the French term forecirct is used for vegetation typesthat extend much further north than does thevegetation that the English call lsquoforestrsquo The Foodand Agriculture Organisation (FAO) definition offorest ie land with more than 10 per cent treecrown cover of trees more than 5 metres high (FAO2001) seems to follow the French lsquoforecirctrsquo but is inno accordance to what Oxfordian botanists likeWhite and AETFAT (Association pour lrsquoEtudeTaxonomique de la Flore drsquoAfrique Tropicale) andUNESCO term lsquoforestrsquo This leads to very confusingstatistics eg Cocircte drsquoIvoire has about 7 million haof forest according to FAO definitions but only 2million ha of high forest as British terminologywould define it while 13 million ha of forest aresaid to exist in Mali (FAO 2001) In consequenceFAOrsquos figures concerning deforestation relate in noway to changes in rain forest cover
Figure 1 shows the forest zone as mapped by White(1983 black line) and as based on NOAA satelliteimages (Olesen 1994 light grey) The forest cover in1992 based on the same images (Olesen 1994) isshown in dark grey It is worth noting in particularthe difference between the two forest zoneboundaries in Sierra Leone White restricted the zoneto the existing continuous forest cover and thus justcovered the Gola forests of the extreme south-east ofthe country In contrast in the interpretation of theNOAA satellite image the entire southern half ofSierra Leone is classified as forest zone fallow Coastalsavannas in Liberia are also more restricted accordingto the satellite imagery than as mapped by White Ineastern Cocircte drsquoIvoire and Togo White included areaswithin the Guineo-Congolian forest domain wherethe satellite can no longer detect any forest fallowSouthern Benin is classified as part of the forest zoneso the so-called lsquoDahomey gaprsquo of savanna there(according to earlier analyses) appears in reality moreas a lsquosouth-east Ghana-Togo gaprsquo Not allclassifications of satellite imagery whether usingNOAA or SPOT (Satellite Pour lrsquoObservation de laTerre) vegetation 1 km-resolution show the forestzone as clearly as Olesen (1994) nor in the sameplaces Some precaution is therefore needed beforeusing such images to alter definitively how theboundaries of the Guineo-Congolian forest domainand its Upper Guinean epicentre are drawn
In Ghana the current forest area corresponds wellwith the actual forest reserves and national parks
32
Hawthorne and Abu-Juam (1995) assessed thecondition of all 214 Ghanaian forest reserves withregard to farming logging and fire impact Sixcondition classes were defined ranging fromlsquoexcellentrsquo to lsquono significant forest leftrsquo (althoughwhether these areas carried forest cover at the timeof their reservation is debatable see Fairhead andLeach 1998) Except for the least forested classessatellite imagery could not detect the differences incondition so for sustainable forest and protectedarea management this important information has tobe collected lsquoon the groundrsquo
3 The gradual nature of changesin species compositionAlthough vegetation maps may suggest that so-called lsquoclimaxrsquo forest types are uniform over theirrange the reality is much more complexFurthermore forest cover maps produced fromsatellite images (as in Figure 1) represent presentforest cover in a uniform colour while followingRichards (1964) some people talk about lsquothetropical rain forestrsquo After Oldeman (1990)however I prefer always to use the plural formlsquotropical rain forestsrsquo in recognition of the hugevariation and many exceptions that exist in what isone of the most complex ecosystems in the worldBotanical studies (Hall and Swaine 1981 VanRompaey 1993) now show that species compositionchanges continuously and gradually both locally inthe landscape and regionally along climaticgradients Most of the species in West Africarsquos rain
forests respond strongly to water availability orinversely to drought stress (Bongers et al 1999)although climate interacts with other factors such assoil type Thus badly distributed rainfall may resultin drier forest types or savanna such as occurs inparts of north-west Liberia through to Conakry onthe coast of the Republic of Guinea Howeverparent soil material such as the schists of easternCocircte drsquoIvoire give clayey soils that allow wetterforest types to survive even when rainfall is lessabundant In the south of Taiuml National Park in CocirctedrsquoIvoire Van Rompaey (1993) found semi-deciduous forests on granite bedrock with manyboulders at the surface similar to the forests foundin the north of the Park on gneissic bedrock Somekilometres eastward across the geological fault trulyevergreen forests existed on schist parent materialSuch mosaic patterns exist at the meso-scale inmany parts of the Upper Guinea region
Figure 2 shows a new regional forest gradient mapfor West Africa (Van Rompaey 2001) preparedusing national timber inventory data (more than 3million measured trees) This was processed in astandardised way using ordination techniques andspatially represented using a GeographicalInformation System (GIS)
In central Cocircte drsquoIvoire a V-shaped incursion ofwoodland and grassland exists within the forestzone called the V-Baouleacute after the people livingthere East of the V-Baouleacute the majority of theforests are of the drier semi-deciduous type
33
Figure 1 West Africa Forest cover in 1992 and forest zone according to Whitersquos (1983) map of vegetationand NOAA satellite imagery (Olesen 1994)
Renaat
Geplaatste afbeelding
whereas west of the V-Baouleacute this type becomesrare In coastal Liberia vast tracts of very humidevergreen forest exist of a type that is absent evenfrom Ghana and that is found only in south-eastNigeria and west Cameroon the Biafran forests richin Caesalpinioideae tree species
Hall and Swaine (1981) Hawthorne (1995) andrecent studies by the ECOSYN project (Universitiesof Wageningen Cocody-Abidjan Oxford) haveshown that these wetter forest types have higherspecies diversity are richer in rare and endemicspecies and can be considered as Pleistocenerefugia ie areas where forest species survived thecolder and drier spells in the Quaternary past
4 From the lsquovirgin forest conceptrsquoto lsquoperpetuity of disturbancersquo andthe different response strategiesof species
There was a time when vegetation ecologists triedto distinguish between primary and late secondaryforests in West Africa At the moment the majordistinction is between unlogged and logged forestas traces of anthropogenic disturbance have beendiscovered in almost all African forest ecosystems(Schwartz 1992 Maley infra White 2001)
In fact in Ghana Hawthorne (1996) recognisedthat in semi-deciduous forests many canopy treespecies are light-demanding or pioneer incharacter suggesting that the forests haveexperienced a heavier disturbance regime than inwetter forests (Figure 3a) The disturbance in thiszone in the past has mainly been climatic Over thelast million years this part of the forest zone hasexperienced a dramatic oscillation of dry and wetspells with dry phases being the most frequent (seeMaley infra) In this respect the semi-deciduousforest is a recently installed forest and this explainsthe abundance of pioneer and light-demandingspecies and the quasi-absence of rare and endemicspecies Hawthorne (1996) expressed this using aGenetic Heat Index corresponding to the averagerarity of the species in a forest (see Figure 3b)Anthropogenic disturbance from farming treefelling and road construction for example areexperienced by the tree species as the forest climategets drier At the same time forest fires burn litteron the forest floor which can improve conditionsfor seed germination and seedling installationwhile fires sometimes induce mast fruiting of trees
The regeneration strategy of these light-demandingspecies is one of discontinuous waves of highlysuccessful seedlings Thus they frequently lack thesmooth exponential size class distribution which
34
Figure 2 Forest vegetation gradient map based on species composition of timber trees from nationalinventories (Van Rompaey 2001) Forest reserves and national parks are shown in white or black outline
Renaat
Geplaatste afbeelding
35
Figure 3(a) Positive correlation between percentage of species with a pioneer character (Pioneer index)and the position of the forest in question along the wet-dry gradient (Hall and Swaine 1981 axis 1 score)in Ghana (Hawthorne 1996)
Figure 3(b) Negative correlation between average rarity of the species (Genetic Heat Index) and positionof the forest on the wet-dry gradient The very dry forests contain very few species so the index values aremore scattered
Renaat
Geplaatste afbeelding
older analytics in forest ecology would haveexpected comprising very many seedlings manysaplings and fewer larger trees This makes theirregeneration difficult to predict and theirsustainable forest management hard to model Forexample one can compare the pioneer timber treesMilicia regia and excelsa (Figure 4) mainly found indrier forests with the shade-bearing tree Tarrietiautilis synonymous with Heritiera utilis (Figure 4)from the wet forests The light-demandingness ofspecies like Heritiera shifts from shade-bearing inyouth to growing in full light when mature Miliciatrees were always found growing in sunlitconditions in the Ghana timber inventoryregardless of age (Hawthorne 1995)
The light-demandingness of a species can also beread from the form of the size class distributionsteeply exponential for shade-bearers to flatlyexponential or irregular for pioneers (Figure 4)Tarrietia and Milicia have equal densities among thebig trees of the respectively wet and dry forestswhere they occur but in the small size class in wetevergreen forests Tarrietia is very abundant Miliciasaplings (5ndash30 cm diameter) and young trees(30ndash60 cm diameter) are ten times rarer in dry semi-deciduous forest and moreover they grow in sunlitplaces which are often more difficult to walkthrough These densities seem to be sufficient forboth species to survive in the forests where they livealthough Alder (1990) was unable to model a stablepopulation from the mortality and growth data from
Ghana that he processed An explanation may bethat successful regeneration only occurs within atime frame of several decades which is beyond themeasuring period of the Ghana Forest Service
5 Conclusion no uniform rainforest zone but two clearlydifferent systemsThe rain forest zone is clearly not a uniform cover ofundisturbed forest Rather present-day speciescomposition reflects both past disturbance regimesand gradients of water availability as they interact witha complex of other factors including soil types andland use While the outcomes of these interactingfactors are highly variable over space and time it ispossible to identify two poles within the forest zone
l Forests with continuous water availabilitythanks to a fairly constant climate andor waterretaining soils evergreen forests rich in rare andendemic species because there has been littleneed for the species to migrate and fewextinction events
l Forests with a long history of climaticdisturbance with irregular water availability anda climate with irregular dry spells semi-deciduousforests with few rare species and little endemism
These distinctions have important implications forrain forest conservation and management The
36
Figure 4 Size class distribution of the pioneer trees Milicia spp in dry semi-deciduous forest and the shade-bearer Tarrietia utilis in wet evergreen forest (Ghana national timber inventory Hawthorne 1995)
evergreen forests are of the highest conservationpriority and by fortuitous chance also contain fewertimber species of high economic value The semi-deciduous forests are of lower conservation priorityfor the sake of rare and endangered species althoughthe currently-undisturbed form of these forests hasbecome very rare and thus merits protection at anumber of places These forests have many timberspecies of high economic value and are thus ofgreatest value from a timber productivity perspective
51 Implications for conservationpriority setting
From Figure 2 it appears that the protected areasand forest reserves within the Upper Guinea regionare spread over the vegetation gradient in a ratheruneven way For example
l Sapo National Park is the only representative ofthe very wet evergreen forests of Liberia
l The Nimba Reserves in southern GuineaLiberia and Cocircte drsquoIvoire are the only protectedupland evergreen forests
l Taiuml Azagny and Banco National Parks (CocirctedrsquoIvoire) and Nini-Suhien National Park(Ghana) contain wet and transitional foresttypes while Bia and Kakum National Parks inGhana are transitional forests
l Marahoueacute National Park contains the driestsemi-deciduous forest at its boundary towoodland and secondary grassland This typeis also found in forest patches in ComoeacuteNational Park in north-east Cocircte drsquoIvoire
This overview therefore suggests that if forestconservation strategies are to represent the regionrsquos
forest types accurately Liberia should give protectedarea status to more of its very wet forests especiallyin the high rainfall zone (4000 mm rain annually) ineastern Liberia extending some 100 km inland fromthe coast Equally more upland evergreen orsubmontane forests in Liberia Guinea Cocircte drsquoIvoire(eg the Monts de Dan) and Ghana (eg the Atewarange Hawthorne and Abu-Juam 1995) deserveprotected area status Furthermore the driest forestsespecially in Ghana where they contain several localendemics might be seen to merit more conservationattention especially where they are under threatfrom fire timber and firewood logging
In short recent perspectives and research invegetation ecology make forests in West Africaharder to classify and the classes harder to map thanwas thought before Many tree species show survivalstrategies that allow them to deal with heavydisturbance whether of climatic or anthropogenicorigin When deciding on conservation andsustainable management options for these forestsevergreen and semi-deciduous forests show highlycontrasted opportunities while both representvariable and dynamic ecosystems which challengeearlier management models based on ideas of stablepopulations and regeneration patterns
Notes I should like to thank Melissa Leach and James
Fairhead for inviting me to the inspiring Brightonworkshop My research in West Africa has beenfunded by Wageningen University (1987ndash1993) andthe European Commission DG Dev ECOSYNProject (1996ndash2000) Many GIS layers have beenprovided by Conservation International Washingtonand WCMC Cambridge I also thank MPE Parrenfor useful comments on the manuscript and WDHawthorne for many discussions about these topicsThe author can be contacted onRenaatVanRompaeyULBacbe
37
ReferencesAlcamo J Leemans R and Kreileman E 1998
lsquoGlobal change scenarios of the 21st centuryrsquoResults from the IMAGE 21 Model KidlingtonPergamon
Alder D 1990 Ghafosim a projection system fornatural forest growth and yield in Ghana OxfordManas Systems Ltd
Aubreacuteville A 1938 lsquoLa forecirct coloniale Les forecircts delrsquoAfrique occidentale franccedilaisersquo Annales de lrsquoAcadeacutemiedes sciences coloniales tome IX Soc drsquoeacuteditionsgeacuteographiques maritimes et coloniales ParislrsquoAcadeacutemie des Sciences
Bongers F Poorter L Van Rompaey RSAR andParren MPE 1999 lsquoDistribution of twelve moistforest canopy tree species in Liberia and Cocircte
drsquoIvoire response curves to a climatic gradientrsquoJournal of Vegetation Science Vol 10 371ndash82
Dawkins HC 1958 The Management of NaturalTropical High-forest with Special Reference to UgandaInstitute Paper No 34 Imperial Forestry InstituteUniversity of Oxford Oxford
Elenga H Peyron O Bonnefille R Jolly DCheddadi R Guiot J Andrieu V Bottema SBuchet G De Beaulieu J-L Hamilton ACMaley J Marchant R Perez-Obiol R Reille MRiollet G Scott L Straka H Taylor D VanCampo E Vincens A Laarif F Jonson H 2000lsquoPollen-based biome reconstruction for southernEurope and Africa 18000 yr BCrsquo Journal ofBiogeography Vol 27 621ndash34
Fairhead J and Leach M 1998 ReframingDeforestation global analyses and local realitiesstudies in West Africa London Routledge
Gueacutehi JI 1993 lsquoLa politique coloniale de protection dela nature en Cocircte drsquoIvoire (1900ndash1958)rsquo in JPouchepadass (ed) Colonisations et environnementBibliothegraveque drsquohistoire drsquooutre mer Nouvelle seacuterie Etudes13 Paris Soc fr drsquohistoire drsquooutre-mer 83ndash104
Guillaumet JL and Adjanohoun E 1971 lsquoLaveacutegeacutetation de la Cocircte drsquoIvoire Dans Le milieunaturel de la Cocircte drsquoIvoirersquo Meacutemoires ORSTOM No50 156ndash263
Hall JB and Swaine MD 1981 lsquoDistribution andecology of vascular plants in a tropical rain forestforest vegetation in Ghanarsquo Geobotany 1 TheHague Dr W Junk Publishers
Hawthorne W and Abu-Juam M 1995 ForestProtection in Ghana Gland IUCN
Hawthorne WD 1995 lsquoEcological profiles of theforest trees of Ghanarsquo Tropical Forests papers No 26Oxford Forestry Institute
Hawthorne WD 1996 lsquoHoles and the sums of partsin Ghanaian forest regeneration scale andsustainable usersquo Proceedings of the Royal SocietyEdinburgh Vol 104B 75ndash176
Jolly D Prentice C Bonnefille R Ballouche ABengo M Brenac P Buchet G Burney D CazetJ-P Cheddadi R Edorh T Elenga HElmoutaki S Guiot J Laarif F Lamb H LezineA-M Maley J Mbenza M Peyron O Reille MReynaud-Farrera I Riollet G Ritchie C RocheE Scott L Ssemmanda I Straka H Umer HVan Campo E Vilimumbalo S Vincens AWaller M 1998 lsquoBiome reconstruction from
pollen and plant macrofossil data for Africa and theArabian peninsula at 0 and 6000 yearsrsquo Journal ofBiogeography Vol 25 1007ndash27
Maley J 1996 lsquoThe African rain forest ndash maincharacteristics of changes in vegetation and climatefrom the Upper Cretaceous to the QuaternaryrsquoProceedings of the Royal Society Edinburgh Vol 104B31ndash73
Oldeman RAA 1990 Forests Elements of SilvologyHeidelberg Springer Verlag
Olesen HH 1994 lsquoTropical forest inventory usingAVHRR-HRPT and LAC data in West Africarsquo FinalReport on Contract No 5088-92-11 ED ISP CHGeneva UNEP-GRID
Parren MPE 1994 lsquoFrench and British colonialforest policies past and present implications forCocircte drsquoIvoire and Ghanarsquo Working Papers in AfricanStudies No 188 Boston African Studies CenterBoston University
Richards PW 1964 The Tropical Rain Forest Anecological study Cambridge Cambridge UniversityPress
Schwartz D 1992 lsquoAssegravechement climatique vers3000 BP et expansion Bantu en Afrique centraleatlantique quelques reacuteflexionsrsquo Bulletin de la SocieteGeacuteologique de France Vol 163 No 3 353ndash61
Van Rompaey RSAR 1993 lsquoForest gradients inWest Africa A spatial gradient analysisrsquo Doctoralthesis Department of Forestry AgriculturalUniversity Wageningen
Van Rompaey RSAR 2001 lsquoMegatransects inUpper Guinea how forest inventory data can beprocessed into a gradient maprsquo in Robbrechts Eand Degreef J (eds) Proceedings XVIth AETFATConference August 2000 Meise Belgium
White F 1983 lsquoThe vegetation of Africa a descriptivememoir to accompany the UNESCOAETFATUNSO vegetation map of Africarsquo Natural ResourcesResearch Paris UNESCO Vol XX
White F 1986 lsquoLa veacutegeacutetation de lrsquoAfrique meacutemoiresaccompagnant la carte de veacutegeacutetation de lrsquoAfriquersquo(UNESCOAETFATUNSO) ORSTOMUNESCORecherches sur les ressources naturelles Vol XX
White LJT 2001 lsquoForest-savanna dynamics and theorigins of lsquoMarantaceae Forestrsquo in central Gabonrsquo inB Weber LJT White A Vedder and L Naughton(eds) African Rain Forest Ecology and ConservationYale Yale University Press
Whitmore TC 1975 Tropical Rain Forests of the FarEast Oxford Clarendon Press
38
Hawthorne and Abu-Juam (1995) assessed thecondition of all 214 Ghanaian forest reserves withregard to farming logging and fire impact Sixcondition classes were defined ranging fromlsquoexcellentrsquo to lsquono significant forest leftrsquo (althoughwhether these areas carried forest cover at the timeof their reservation is debatable see Fairhead andLeach 1998) Except for the least forested classessatellite imagery could not detect the differences incondition so for sustainable forest and protectedarea management this important information has tobe collected lsquoon the groundrsquo
3 The gradual nature of changesin species compositionAlthough vegetation maps may suggest that so-called lsquoclimaxrsquo forest types are uniform over theirrange the reality is much more complexFurthermore forest cover maps produced fromsatellite images (as in Figure 1) represent presentforest cover in a uniform colour while followingRichards (1964) some people talk about lsquothetropical rain forestrsquo After Oldeman (1990)however I prefer always to use the plural formlsquotropical rain forestsrsquo in recognition of the hugevariation and many exceptions that exist in what isone of the most complex ecosystems in the worldBotanical studies (Hall and Swaine 1981 VanRompaey 1993) now show that species compositionchanges continuously and gradually both locally inthe landscape and regionally along climaticgradients Most of the species in West Africarsquos rain
forests respond strongly to water availability orinversely to drought stress (Bongers et al 1999)although climate interacts with other factors such assoil type Thus badly distributed rainfall may resultin drier forest types or savanna such as occurs inparts of north-west Liberia through to Conakry onthe coast of the Republic of Guinea Howeverparent soil material such as the schists of easternCocircte drsquoIvoire give clayey soils that allow wetterforest types to survive even when rainfall is lessabundant In the south of Taiuml National Park in CocirctedrsquoIvoire Van Rompaey (1993) found semi-deciduous forests on granite bedrock with manyboulders at the surface similar to the forests foundin the north of the Park on gneissic bedrock Somekilometres eastward across the geological fault trulyevergreen forests existed on schist parent materialSuch mosaic patterns exist at the meso-scale inmany parts of the Upper Guinea region
Figure 2 shows a new regional forest gradient mapfor West Africa (Van Rompaey 2001) preparedusing national timber inventory data (more than 3million measured trees) This was processed in astandardised way using ordination techniques andspatially represented using a GeographicalInformation System (GIS)
In central Cocircte drsquoIvoire a V-shaped incursion ofwoodland and grassland exists within the forestzone called the V-Baouleacute after the people livingthere East of the V-Baouleacute the majority of theforests are of the drier semi-deciduous type
33
Figure 1 West Africa Forest cover in 1992 and forest zone according to Whitersquos (1983) map of vegetationand NOAA satellite imagery (Olesen 1994)
Renaat
Geplaatste afbeelding
whereas west of the V-Baouleacute this type becomesrare In coastal Liberia vast tracts of very humidevergreen forest exist of a type that is absent evenfrom Ghana and that is found only in south-eastNigeria and west Cameroon the Biafran forests richin Caesalpinioideae tree species
Hall and Swaine (1981) Hawthorne (1995) andrecent studies by the ECOSYN project (Universitiesof Wageningen Cocody-Abidjan Oxford) haveshown that these wetter forest types have higherspecies diversity are richer in rare and endemicspecies and can be considered as Pleistocenerefugia ie areas where forest species survived thecolder and drier spells in the Quaternary past
4 From the lsquovirgin forest conceptrsquoto lsquoperpetuity of disturbancersquo andthe different response strategiesof species
There was a time when vegetation ecologists triedto distinguish between primary and late secondaryforests in West Africa At the moment the majordistinction is between unlogged and logged forestas traces of anthropogenic disturbance have beendiscovered in almost all African forest ecosystems(Schwartz 1992 Maley infra White 2001)
In fact in Ghana Hawthorne (1996) recognisedthat in semi-deciduous forests many canopy treespecies are light-demanding or pioneer incharacter suggesting that the forests haveexperienced a heavier disturbance regime than inwetter forests (Figure 3a) The disturbance in thiszone in the past has mainly been climatic Over thelast million years this part of the forest zone hasexperienced a dramatic oscillation of dry and wetspells with dry phases being the most frequent (seeMaley infra) In this respect the semi-deciduousforest is a recently installed forest and this explainsthe abundance of pioneer and light-demandingspecies and the quasi-absence of rare and endemicspecies Hawthorne (1996) expressed this using aGenetic Heat Index corresponding to the averagerarity of the species in a forest (see Figure 3b)Anthropogenic disturbance from farming treefelling and road construction for example areexperienced by the tree species as the forest climategets drier At the same time forest fires burn litteron the forest floor which can improve conditionsfor seed germination and seedling installationwhile fires sometimes induce mast fruiting of trees
The regeneration strategy of these light-demandingspecies is one of discontinuous waves of highlysuccessful seedlings Thus they frequently lack thesmooth exponential size class distribution which
34
Figure 2 Forest vegetation gradient map based on species composition of timber trees from nationalinventories (Van Rompaey 2001) Forest reserves and national parks are shown in white or black outline
Renaat
Geplaatste afbeelding
35
Figure 3(a) Positive correlation between percentage of species with a pioneer character (Pioneer index)and the position of the forest in question along the wet-dry gradient (Hall and Swaine 1981 axis 1 score)in Ghana (Hawthorne 1996)
Figure 3(b) Negative correlation between average rarity of the species (Genetic Heat Index) and positionof the forest on the wet-dry gradient The very dry forests contain very few species so the index values aremore scattered
Renaat
Geplaatste afbeelding
older analytics in forest ecology would haveexpected comprising very many seedlings manysaplings and fewer larger trees This makes theirregeneration difficult to predict and theirsustainable forest management hard to model Forexample one can compare the pioneer timber treesMilicia regia and excelsa (Figure 4) mainly found indrier forests with the shade-bearing tree Tarrietiautilis synonymous with Heritiera utilis (Figure 4)from the wet forests The light-demandingness ofspecies like Heritiera shifts from shade-bearing inyouth to growing in full light when mature Miliciatrees were always found growing in sunlitconditions in the Ghana timber inventoryregardless of age (Hawthorne 1995)
The light-demandingness of a species can also beread from the form of the size class distributionsteeply exponential for shade-bearers to flatlyexponential or irregular for pioneers (Figure 4)Tarrietia and Milicia have equal densities among thebig trees of the respectively wet and dry forestswhere they occur but in the small size class in wetevergreen forests Tarrietia is very abundant Miliciasaplings (5ndash30 cm diameter) and young trees(30ndash60 cm diameter) are ten times rarer in dry semi-deciduous forest and moreover they grow in sunlitplaces which are often more difficult to walkthrough These densities seem to be sufficient forboth species to survive in the forests where they livealthough Alder (1990) was unable to model a stablepopulation from the mortality and growth data from
Ghana that he processed An explanation may bethat successful regeneration only occurs within atime frame of several decades which is beyond themeasuring period of the Ghana Forest Service
5 Conclusion no uniform rainforest zone but two clearlydifferent systemsThe rain forest zone is clearly not a uniform cover ofundisturbed forest Rather present-day speciescomposition reflects both past disturbance regimesand gradients of water availability as they interact witha complex of other factors including soil types andland use While the outcomes of these interactingfactors are highly variable over space and time it ispossible to identify two poles within the forest zone
l Forests with continuous water availabilitythanks to a fairly constant climate andor waterretaining soils evergreen forests rich in rare andendemic species because there has been littleneed for the species to migrate and fewextinction events
l Forests with a long history of climaticdisturbance with irregular water availability anda climate with irregular dry spells semi-deciduousforests with few rare species and little endemism
These distinctions have important implications forrain forest conservation and management The
36
Figure 4 Size class distribution of the pioneer trees Milicia spp in dry semi-deciduous forest and the shade-bearer Tarrietia utilis in wet evergreen forest (Ghana national timber inventory Hawthorne 1995)
evergreen forests are of the highest conservationpriority and by fortuitous chance also contain fewertimber species of high economic value The semi-deciduous forests are of lower conservation priorityfor the sake of rare and endangered species althoughthe currently-undisturbed form of these forests hasbecome very rare and thus merits protection at anumber of places These forests have many timberspecies of high economic value and are thus ofgreatest value from a timber productivity perspective
51 Implications for conservationpriority setting
From Figure 2 it appears that the protected areasand forest reserves within the Upper Guinea regionare spread over the vegetation gradient in a ratheruneven way For example
l Sapo National Park is the only representative ofthe very wet evergreen forests of Liberia
l The Nimba Reserves in southern GuineaLiberia and Cocircte drsquoIvoire are the only protectedupland evergreen forests
l Taiuml Azagny and Banco National Parks (CocirctedrsquoIvoire) and Nini-Suhien National Park(Ghana) contain wet and transitional foresttypes while Bia and Kakum National Parks inGhana are transitional forests
l Marahoueacute National Park contains the driestsemi-deciduous forest at its boundary towoodland and secondary grassland This typeis also found in forest patches in ComoeacuteNational Park in north-east Cocircte drsquoIvoire
This overview therefore suggests that if forestconservation strategies are to represent the regionrsquos
forest types accurately Liberia should give protectedarea status to more of its very wet forests especiallyin the high rainfall zone (4000 mm rain annually) ineastern Liberia extending some 100 km inland fromthe coast Equally more upland evergreen orsubmontane forests in Liberia Guinea Cocircte drsquoIvoire(eg the Monts de Dan) and Ghana (eg the Atewarange Hawthorne and Abu-Juam 1995) deserveprotected area status Furthermore the driest forestsespecially in Ghana where they contain several localendemics might be seen to merit more conservationattention especially where they are under threatfrom fire timber and firewood logging
In short recent perspectives and research invegetation ecology make forests in West Africaharder to classify and the classes harder to map thanwas thought before Many tree species show survivalstrategies that allow them to deal with heavydisturbance whether of climatic or anthropogenicorigin When deciding on conservation andsustainable management options for these forestsevergreen and semi-deciduous forests show highlycontrasted opportunities while both representvariable and dynamic ecosystems which challengeearlier management models based on ideas of stablepopulations and regeneration patterns
Notes I should like to thank Melissa Leach and James
Fairhead for inviting me to the inspiring Brightonworkshop My research in West Africa has beenfunded by Wageningen University (1987ndash1993) andthe European Commission DG Dev ECOSYNProject (1996ndash2000) Many GIS layers have beenprovided by Conservation International Washingtonand WCMC Cambridge I also thank MPE Parrenfor useful comments on the manuscript and WDHawthorne for many discussions about these topicsThe author can be contacted onRenaatVanRompaeyULBacbe
37
ReferencesAlcamo J Leemans R and Kreileman E 1998
lsquoGlobal change scenarios of the 21st centuryrsquoResults from the IMAGE 21 Model KidlingtonPergamon
Alder D 1990 Ghafosim a projection system fornatural forest growth and yield in Ghana OxfordManas Systems Ltd
Aubreacuteville A 1938 lsquoLa forecirct coloniale Les forecircts delrsquoAfrique occidentale franccedilaisersquo Annales de lrsquoAcadeacutemiedes sciences coloniales tome IX Soc drsquoeacuteditionsgeacuteographiques maritimes et coloniales ParislrsquoAcadeacutemie des Sciences
Bongers F Poorter L Van Rompaey RSAR andParren MPE 1999 lsquoDistribution of twelve moistforest canopy tree species in Liberia and Cocircte
drsquoIvoire response curves to a climatic gradientrsquoJournal of Vegetation Science Vol 10 371ndash82
Dawkins HC 1958 The Management of NaturalTropical High-forest with Special Reference to UgandaInstitute Paper No 34 Imperial Forestry InstituteUniversity of Oxford Oxford
Elenga H Peyron O Bonnefille R Jolly DCheddadi R Guiot J Andrieu V Bottema SBuchet G De Beaulieu J-L Hamilton ACMaley J Marchant R Perez-Obiol R Reille MRiollet G Scott L Straka H Taylor D VanCampo E Vincens A Laarif F Jonson H 2000lsquoPollen-based biome reconstruction for southernEurope and Africa 18000 yr BCrsquo Journal ofBiogeography Vol 27 621ndash34
Fairhead J and Leach M 1998 ReframingDeforestation global analyses and local realitiesstudies in West Africa London Routledge
Gueacutehi JI 1993 lsquoLa politique coloniale de protection dela nature en Cocircte drsquoIvoire (1900ndash1958)rsquo in JPouchepadass (ed) Colonisations et environnementBibliothegraveque drsquohistoire drsquooutre mer Nouvelle seacuterie Etudes13 Paris Soc fr drsquohistoire drsquooutre-mer 83ndash104
Guillaumet JL and Adjanohoun E 1971 lsquoLaveacutegeacutetation de la Cocircte drsquoIvoire Dans Le milieunaturel de la Cocircte drsquoIvoirersquo Meacutemoires ORSTOM No50 156ndash263
Hall JB and Swaine MD 1981 lsquoDistribution andecology of vascular plants in a tropical rain forestforest vegetation in Ghanarsquo Geobotany 1 TheHague Dr W Junk Publishers
Hawthorne W and Abu-Juam M 1995 ForestProtection in Ghana Gland IUCN
Hawthorne WD 1995 lsquoEcological profiles of theforest trees of Ghanarsquo Tropical Forests papers No 26Oxford Forestry Institute
Hawthorne WD 1996 lsquoHoles and the sums of partsin Ghanaian forest regeneration scale andsustainable usersquo Proceedings of the Royal SocietyEdinburgh Vol 104B 75ndash176
Jolly D Prentice C Bonnefille R Ballouche ABengo M Brenac P Buchet G Burney D CazetJ-P Cheddadi R Edorh T Elenga HElmoutaki S Guiot J Laarif F Lamb H LezineA-M Maley J Mbenza M Peyron O Reille MReynaud-Farrera I Riollet G Ritchie C RocheE Scott L Ssemmanda I Straka H Umer HVan Campo E Vilimumbalo S Vincens AWaller M 1998 lsquoBiome reconstruction from
pollen and plant macrofossil data for Africa and theArabian peninsula at 0 and 6000 yearsrsquo Journal ofBiogeography Vol 25 1007ndash27
Maley J 1996 lsquoThe African rain forest ndash maincharacteristics of changes in vegetation and climatefrom the Upper Cretaceous to the QuaternaryrsquoProceedings of the Royal Society Edinburgh Vol 104B31ndash73
Oldeman RAA 1990 Forests Elements of SilvologyHeidelberg Springer Verlag
Olesen HH 1994 lsquoTropical forest inventory usingAVHRR-HRPT and LAC data in West Africarsquo FinalReport on Contract No 5088-92-11 ED ISP CHGeneva UNEP-GRID
Parren MPE 1994 lsquoFrench and British colonialforest policies past and present implications forCocircte drsquoIvoire and Ghanarsquo Working Papers in AfricanStudies No 188 Boston African Studies CenterBoston University
Richards PW 1964 The Tropical Rain Forest Anecological study Cambridge Cambridge UniversityPress
Schwartz D 1992 lsquoAssegravechement climatique vers3000 BP et expansion Bantu en Afrique centraleatlantique quelques reacuteflexionsrsquo Bulletin de la SocieteGeacuteologique de France Vol 163 No 3 353ndash61
Van Rompaey RSAR 1993 lsquoForest gradients inWest Africa A spatial gradient analysisrsquo Doctoralthesis Department of Forestry AgriculturalUniversity Wageningen
Van Rompaey RSAR 2001 lsquoMegatransects inUpper Guinea how forest inventory data can beprocessed into a gradient maprsquo in Robbrechts Eand Degreef J (eds) Proceedings XVIth AETFATConference August 2000 Meise Belgium
White F 1983 lsquoThe vegetation of Africa a descriptivememoir to accompany the UNESCOAETFATUNSO vegetation map of Africarsquo Natural ResourcesResearch Paris UNESCO Vol XX
White F 1986 lsquoLa veacutegeacutetation de lrsquoAfrique meacutemoiresaccompagnant la carte de veacutegeacutetation de lrsquoAfriquersquo(UNESCOAETFATUNSO) ORSTOMUNESCORecherches sur les ressources naturelles Vol XX
White LJT 2001 lsquoForest-savanna dynamics and theorigins of lsquoMarantaceae Forestrsquo in central Gabonrsquo inB Weber LJT White A Vedder and L Naughton(eds) African Rain Forest Ecology and ConservationYale Yale University Press
Whitmore TC 1975 Tropical Rain Forests of the FarEast Oxford Clarendon Press
38
whereas west of the V-Baouleacute this type becomesrare In coastal Liberia vast tracts of very humidevergreen forest exist of a type that is absent evenfrom Ghana and that is found only in south-eastNigeria and west Cameroon the Biafran forests richin Caesalpinioideae tree species
Hall and Swaine (1981) Hawthorne (1995) andrecent studies by the ECOSYN project (Universitiesof Wageningen Cocody-Abidjan Oxford) haveshown that these wetter forest types have higherspecies diversity are richer in rare and endemicspecies and can be considered as Pleistocenerefugia ie areas where forest species survived thecolder and drier spells in the Quaternary past
4 From the lsquovirgin forest conceptrsquoto lsquoperpetuity of disturbancersquo andthe different response strategiesof species
There was a time when vegetation ecologists triedto distinguish between primary and late secondaryforests in West Africa At the moment the majordistinction is between unlogged and logged forestas traces of anthropogenic disturbance have beendiscovered in almost all African forest ecosystems(Schwartz 1992 Maley infra White 2001)
In fact in Ghana Hawthorne (1996) recognisedthat in semi-deciduous forests many canopy treespecies are light-demanding or pioneer incharacter suggesting that the forests haveexperienced a heavier disturbance regime than inwetter forests (Figure 3a) The disturbance in thiszone in the past has mainly been climatic Over thelast million years this part of the forest zone hasexperienced a dramatic oscillation of dry and wetspells with dry phases being the most frequent (seeMaley infra) In this respect the semi-deciduousforest is a recently installed forest and this explainsthe abundance of pioneer and light-demandingspecies and the quasi-absence of rare and endemicspecies Hawthorne (1996) expressed this using aGenetic Heat Index corresponding to the averagerarity of the species in a forest (see Figure 3b)Anthropogenic disturbance from farming treefelling and road construction for example areexperienced by the tree species as the forest climategets drier At the same time forest fires burn litteron the forest floor which can improve conditionsfor seed germination and seedling installationwhile fires sometimes induce mast fruiting of trees
The regeneration strategy of these light-demandingspecies is one of discontinuous waves of highlysuccessful seedlings Thus they frequently lack thesmooth exponential size class distribution which
34
Figure 2 Forest vegetation gradient map based on species composition of timber trees from nationalinventories (Van Rompaey 2001) Forest reserves and national parks are shown in white or black outline
Renaat
Geplaatste afbeelding
35
Figure 3(a) Positive correlation between percentage of species with a pioneer character (Pioneer index)and the position of the forest in question along the wet-dry gradient (Hall and Swaine 1981 axis 1 score)in Ghana (Hawthorne 1996)
Figure 3(b) Negative correlation between average rarity of the species (Genetic Heat Index) and positionof the forest on the wet-dry gradient The very dry forests contain very few species so the index values aremore scattered
Renaat
Geplaatste afbeelding
older analytics in forest ecology would haveexpected comprising very many seedlings manysaplings and fewer larger trees This makes theirregeneration difficult to predict and theirsustainable forest management hard to model Forexample one can compare the pioneer timber treesMilicia regia and excelsa (Figure 4) mainly found indrier forests with the shade-bearing tree Tarrietiautilis synonymous with Heritiera utilis (Figure 4)from the wet forests The light-demandingness ofspecies like Heritiera shifts from shade-bearing inyouth to growing in full light when mature Miliciatrees were always found growing in sunlitconditions in the Ghana timber inventoryregardless of age (Hawthorne 1995)
The light-demandingness of a species can also beread from the form of the size class distributionsteeply exponential for shade-bearers to flatlyexponential or irregular for pioneers (Figure 4)Tarrietia and Milicia have equal densities among thebig trees of the respectively wet and dry forestswhere they occur but in the small size class in wetevergreen forests Tarrietia is very abundant Miliciasaplings (5ndash30 cm diameter) and young trees(30ndash60 cm diameter) are ten times rarer in dry semi-deciduous forest and moreover they grow in sunlitplaces which are often more difficult to walkthrough These densities seem to be sufficient forboth species to survive in the forests where they livealthough Alder (1990) was unable to model a stablepopulation from the mortality and growth data from
Ghana that he processed An explanation may bethat successful regeneration only occurs within atime frame of several decades which is beyond themeasuring period of the Ghana Forest Service
5 Conclusion no uniform rainforest zone but two clearlydifferent systemsThe rain forest zone is clearly not a uniform cover ofundisturbed forest Rather present-day speciescomposition reflects both past disturbance regimesand gradients of water availability as they interact witha complex of other factors including soil types andland use While the outcomes of these interactingfactors are highly variable over space and time it ispossible to identify two poles within the forest zone
l Forests with continuous water availabilitythanks to a fairly constant climate andor waterretaining soils evergreen forests rich in rare andendemic species because there has been littleneed for the species to migrate and fewextinction events
l Forests with a long history of climaticdisturbance with irregular water availability anda climate with irregular dry spells semi-deciduousforests with few rare species and little endemism
These distinctions have important implications forrain forest conservation and management The
36
Figure 4 Size class distribution of the pioneer trees Milicia spp in dry semi-deciduous forest and the shade-bearer Tarrietia utilis in wet evergreen forest (Ghana national timber inventory Hawthorne 1995)
evergreen forests are of the highest conservationpriority and by fortuitous chance also contain fewertimber species of high economic value The semi-deciduous forests are of lower conservation priorityfor the sake of rare and endangered species althoughthe currently-undisturbed form of these forests hasbecome very rare and thus merits protection at anumber of places These forests have many timberspecies of high economic value and are thus ofgreatest value from a timber productivity perspective
51 Implications for conservationpriority setting
From Figure 2 it appears that the protected areasand forest reserves within the Upper Guinea regionare spread over the vegetation gradient in a ratheruneven way For example
l Sapo National Park is the only representative ofthe very wet evergreen forests of Liberia
l The Nimba Reserves in southern GuineaLiberia and Cocircte drsquoIvoire are the only protectedupland evergreen forests
l Taiuml Azagny and Banco National Parks (CocirctedrsquoIvoire) and Nini-Suhien National Park(Ghana) contain wet and transitional foresttypes while Bia and Kakum National Parks inGhana are transitional forests
l Marahoueacute National Park contains the driestsemi-deciduous forest at its boundary towoodland and secondary grassland This typeis also found in forest patches in ComoeacuteNational Park in north-east Cocircte drsquoIvoire
This overview therefore suggests that if forestconservation strategies are to represent the regionrsquos
forest types accurately Liberia should give protectedarea status to more of its very wet forests especiallyin the high rainfall zone (4000 mm rain annually) ineastern Liberia extending some 100 km inland fromthe coast Equally more upland evergreen orsubmontane forests in Liberia Guinea Cocircte drsquoIvoire(eg the Monts de Dan) and Ghana (eg the Atewarange Hawthorne and Abu-Juam 1995) deserveprotected area status Furthermore the driest forestsespecially in Ghana where they contain several localendemics might be seen to merit more conservationattention especially where they are under threatfrom fire timber and firewood logging
In short recent perspectives and research invegetation ecology make forests in West Africaharder to classify and the classes harder to map thanwas thought before Many tree species show survivalstrategies that allow them to deal with heavydisturbance whether of climatic or anthropogenicorigin When deciding on conservation andsustainable management options for these forestsevergreen and semi-deciduous forests show highlycontrasted opportunities while both representvariable and dynamic ecosystems which challengeearlier management models based on ideas of stablepopulations and regeneration patterns
Notes I should like to thank Melissa Leach and James
Fairhead for inviting me to the inspiring Brightonworkshop My research in West Africa has beenfunded by Wageningen University (1987ndash1993) andthe European Commission DG Dev ECOSYNProject (1996ndash2000) Many GIS layers have beenprovided by Conservation International Washingtonand WCMC Cambridge I also thank MPE Parrenfor useful comments on the manuscript and WDHawthorne for many discussions about these topicsThe author can be contacted onRenaatVanRompaeyULBacbe
37
ReferencesAlcamo J Leemans R and Kreileman E 1998
lsquoGlobal change scenarios of the 21st centuryrsquoResults from the IMAGE 21 Model KidlingtonPergamon
Alder D 1990 Ghafosim a projection system fornatural forest growth and yield in Ghana OxfordManas Systems Ltd
Aubreacuteville A 1938 lsquoLa forecirct coloniale Les forecircts delrsquoAfrique occidentale franccedilaisersquo Annales de lrsquoAcadeacutemiedes sciences coloniales tome IX Soc drsquoeacuteditionsgeacuteographiques maritimes et coloniales ParislrsquoAcadeacutemie des Sciences
Bongers F Poorter L Van Rompaey RSAR andParren MPE 1999 lsquoDistribution of twelve moistforest canopy tree species in Liberia and Cocircte
drsquoIvoire response curves to a climatic gradientrsquoJournal of Vegetation Science Vol 10 371ndash82
Dawkins HC 1958 The Management of NaturalTropical High-forest with Special Reference to UgandaInstitute Paper No 34 Imperial Forestry InstituteUniversity of Oxford Oxford
Elenga H Peyron O Bonnefille R Jolly DCheddadi R Guiot J Andrieu V Bottema SBuchet G De Beaulieu J-L Hamilton ACMaley J Marchant R Perez-Obiol R Reille MRiollet G Scott L Straka H Taylor D VanCampo E Vincens A Laarif F Jonson H 2000lsquoPollen-based biome reconstruction for southernEurope and Africa 18000 yr BCrsquo Journal ofBiogeography Vol 27 621ndash34
Fairhead J and Leach M 1998 ReframingDeforestation global analyses and local realitiesstudies in West Africa London Routledge
Gueacutehi JI 1993 lsquoLa politique coloniale de protection dela nature en Cocircte drsquoIvoire (1900ndash1958)rsquo in JPouchepadass (ed) Colonisations et environnementBibliothegraveque drsquohistoire drsquooutre mer Nouvelle seacuterie Etudes13 Paris Soc fr drsquohistoire drsquooutre-mer 83ndash104
Guillaumet JL and Adjanohoun E 1971 lsquoLaveacutegeacutetation de la Cocircte drsquoIvoire Dans Le milieunaturel de la Cocircte drsquoIvoirersquo Meacutemoires ORSTOM No50 156ndash263
Hall JB and Swaine MD 1981 lsquoDistribution andecology of vascular plants in a tropical rain forestforest vegetation in Ghanarsquo Geobotany 1 TheHague Dr W Junk Publishers
Hawthorne W and Abu-Juam M 1995 ForestProtection in Ghana Gland IUCN
Hawthorne WD 1995 lsquoEcological profiles of theforest trees of Ghanarsquo Tropical Forests papers No 26Oxford Forestry Institute
Hawthorne WD 1996 lsquoHoles and the sums of partsin Ghanaian forest regeneration scale andsustainable usersquo Proceedings of the Royal SocietyEdinburgh Vol 104B 75ndash176
Jolly D Prentice C Bonnefille R Ballouche ABengo M Brenac P Buchet G Burney D CazetJ-P Cheddadi R Edorh T Elenga HElmoutaki S Guiot J Laarif F Lamb H LezineA-M Maley J Mbenza M Peyron O Reille MReynaud-Farrera I Riollet G Ritchie C RocheE Scott L Ssemmanda I Straka H Umer HVan Campo E Vilimumbalo S Vincens AWaller M 1998 lsquoBiome reconstruction from
pollen and plant macrofossil data for Africa and theArabian peninsula at 0 and 6000 yearsrsquo Journal ofBiogeography Vol 25 1007ndash27
Maley J 1996 lsquoThe African rain forest ndash maincharacteristics of changes in vegetation and climatefrom the Upper Cretaceous to the QuaternaryrsquoProceedings of the Royal Society Edinburgh Vol 104B31ndash73
Oldeman RAA 1990 Forests Elements of SilvologyHeidelberg Springer Verlag
Olesen HH 1994 lsquoTropical forest inventory usingAVHRR-HRPT and LAC data in West Africarsquo FinalReport on Contract No 5088-92-11 ED ISP CHGeneva UNEP-GRID
Parren MPE 1994 lsquoFrench and British colonialforest policies past and present implications forCocircte drsquoIvoire and Ghanarsquo Working Papers in AfricanStudies No 188 Boston African Studies CenterBoston University
Richards PW 1964 The Tropical Rain Forest Anecological study Cambridge Cambridge UniversityPress
Schwartz D 1992 lsquoAssegravechement climatique vers3000 BP et expansion Bantu en Afrique centraleatlantique quelques reacuteflexionsrsquo Bulletin de la SocieteGeacuteologique de France Vol 163 No 3 353ndash61
Van Rompaey RSAR 1993 lsquoForest gradients inWest Africa A spatial gradient analysisrsquo Doctoralthesis Department of Forestry AgriculturalUniversity Wageningen
Van Rompaey RSAR 2001 lsquoMegatransects inUpper Guinea how forest inventory data can beprocessed into a gradient maprsquo in Robbrechts Eand Degreef J (eds) Proceedings XVIth AETFATConference August 2000 Meise Belgium
White F 1983 lsquoThe vegetation of Africa a descriptivememoir to accompany the UNESCOAETFATUNSO vegetation map of Africarsquo Natural ResourcesResearch Paris UNESCO Vol XX
White F 1986 lsquoLa veacutegeacutetation de lrsquoAfrique meacutemoiresaccompagnant la carte de veacutegeacutetation de lrsquoAfriquersquo(UNESCOAETFATUNSO) ORSTOMUNESCORecherches sur les ressources naturelles Vol XX
White LJT 2001 lsquoForest-savanna dynamics and theorigins of lsquoMarantaceae Forestrsquo in central Gabonrsquo inB Weber LJT White A Vedder and L Naughton(eds) African Rain Forest Ecology and ConservationYale Yale University Press
Whitmore TC 1975 Tropical Rain Forests of the FarEast Oxford Clarendon Press
38
35
Figure 3(a) Positive correlation between percentage of species with a pioneer character (Pioneer index)and the position of the forest in question along the wet-dry gradient (Hall and Swaine 1981 axis 1 score)in Ghana (Hawthorne 1996)
Figure 3(b) Negative correlation between average rarity of the species (Genetic Heat Index) and positionof the forest on the wet-dry gradient The very dry forests contain very few species so the index values aremore scattered
Renaat
Geplaatste afbeelding
older analytics in forest ecology would haveexpected comprising very many seedlings manysaplings and fewer larger trees This makes theirregeneration difficult to predict and theirsustainable forest management hard to model Forexample one can compare the pioneer timber treesMilicia regia and excelsa (Figure 4) mainly found indrier forests with the shade-bearing tree Tarrietiautilis synonymous with Heritiera utilis (Figure 4)from the wet forests The light-demandingness ofspecies like Heritiera shifts from shade-bearing inyouth to growing in full light when mature Miliciatrees were always found growing in sunlitconditions in the Ghana timber inventoryregardless of age (Hawthorne 1995)
The light-demandingness of a species can also beread from the form of the size class distributionsteeply exponential for shade-bearers to flatlyexponential or irregular for pioneers (Figure 4)Tarrietia and Milicia have equal densities among thebig trees of the respectively wet and dry forestswhere they occur but in the small size class in wetevergreen forests Tarrietia is very abundant Miliciasaplings (5ndash30 cm diameter) and young trees(30ndash60 cm diameter) are ten times rarer in dry semi-deciduous forest and moreover they grow in sunlitplaces which are often more difficult to walkthrough These densities seem to be sufficient forboth species to survive in the forests where they livealthough Alder (1990) was unable to model a stablepopulation from the mortality and growth data from
Ghana that he processed An explanation may bethat successful regeneration only occurs within atime frame of several decades which is beyond themeasuring period of the Ghana Forest Service
5 Conclusion no uniform rainforest zone but two clearlydifferent systemsThe rain forest zone is clearly not a uniform cover ofundisturbed forest Rather present-day speciescomposition reflects both past disturbance regimesand gradients of water availability as they interact witha complex of other factors including soil types andland use While the outcomes of these interactingfactors are highly variable over space and time it ispossible to identify two poles within the forest zone
l Forests with continuous water availabilitythanks to a fairly constant climate andor waterretaining soils evergreen forests rich in rare andendemic species because there has been littleneed for the species to migrate and fewextinction events
l Forests with a long history of climaticdisturbance with irregular water availability anda climate with irregular dry spells semi-deciduousforests with few rare species and little endemism
These distinctions have important implications forrain forest conservation and management The
36
Figure 4 Size class distribution of the pioneer trees Milicia spp in dry semi-deciduous forest and the shade-bearer Tarrietia utilis in wet evergreen forest (Ghana national timber inventory Hawthorne 1995)
evergreen forests are of the highest conservationpriority and by fortuitous chance also contain fewertimber species of high economic value The semi-deciduous forests are of lower conservation priorityfor the sake of rare and endangered species althoughthe currently-undisturbed form of these forests hasbecome very rare and thus merits protection at anumber of places These forests have many timberspecies of high economic value and are thus ofgreatest value from a timber productivity perspective
51 Implications for conservationpriority setting
From Figure 2 it appears that the protected areasand forest reserves within the Upper Guinea regionare spread over the vegetation gradient in a ratheruneven way For example
l Sapo National Park is the only representative ofthe very wet evergreen forests of Liberia
l The Nimba Reserves in southern GuineaLiberia and Cocircte drsquoIvoire are the only protectedupland evergreen forests
l Taiuml Azagny and Banco National Parks (CocirctedrsquoIvoire) and Nini-Suhien National Park(Ghana) contain wet and transitional foresttypes while Bia and Kakum National Parks inGhana are transitional forests
l Marahoueacute National Park contains the driestsemi-deciduous forest at its boundary towoodland and secondary grassland This typeis also found in forest patches in ComoeacuteNational Park in north-east Cocircte drsquoIvoire
This overview therefore suggests that if forestconservation strategies are to represent the regionrsquos
forest types accurately Liberia should give protectedarea status to more of its very wet forests especiallyin the high rainfall zone (4000 mm rain annually) ineastern Liberia extending some 100 km inland fromthe coast Equally more upland evergreen orsubmontane forests in Liberia Guinea Cocircte drsquoIvoire(eg the Monts de Dan) and Ghana (eg the Atewarange Hawthorne and Abu-Juam 1995) deserveprotected area status Furthermore the driest forestsespecially in Ghana where they contain several localendemics might be seen to merit more conservationattention especially where they are under threatfrom fire timber and firewood logging
In short recent perspectives and research invegetation ecology make forests in West Africaharder to classify and the classes harder to map thanwas thought before Many tree species show survivalstrategies that allow them to deal with heavydisturbance whether of climatic or anthropogenicorigin When deciding on conservation andsustainable management options for these forestsevergreen and semi-deciduous forests show highlycontrasted opportunities while both representvariable and dynamic ecosystems which challengeearlier management models based on ideas of stablepopulations and regeneration patterns
Notes I should like to thank Melissa Leach and James
Fairhead for inviting me to the inspiring Brightonworkshop My research in West Africa has beenfunded by Wageningen University (1987ndash1993) andthe European Commission DG Dev ECOSYNProject (1996ndash2000) Many GIS layers have beenprovided by Conservation International Washingtonand WCMC Cambridge I also thank MPE Parrenfor useful comments on the manuscript and WDHawthorne for many discussions about these topicsThe author can be contacted onRenaatVanRompaeyULBacbe
37
ReferencesAlcamo J Leemans R and Kreileman E 1998
lsquoGlobal change scenarios of the 21st centuryrsquoResults from the IMAGE 21 Model KidlingtonPergamon
Alder D 1990 Ghafosim a projection system fornatural forest growth and yield in Ghana OxfordManas Systems Ltd
Aubreacuteville A 1938 lsquoLa forecirct coloniale Les forecircts delrsquoAfrique occidentale franccedilaisersquo Annales de lrsquoAcadeacutemiedes sciences coloniales tome IX Soc drsquoeacuteditionsgeacuteographiques maritimes et coloniales ParislrsquoAcadeacutemie des Sciences
Bongers F Poorter L Van Rompaey RSAR andParren MPE 1999 lsquoDistribution of twelve moistforest canopy tree species in Liberia and Cocircte
drsquoIvoire response curves to a climatic gradientrsquoJournal of Vegetation Science Vol 10 371ndash82
Dawkins HC 1958 The Management of NaturalTropical High-forest with Special Reference to UgandaInstitute Paper No 34 Imperial Forestry InstituteUniversity of Oxford Oxford
Elenga H Peyron O Bonnefille R Jolly DCheddadi R Guiot J Andrieu V Bottema SBuchet G De Beaulieu J-L Hamilton ACMaley J Marchant R Perez-Obiol R Reille MRiollet G Scott L Straka H Taylor D VanCampo E Vincens A Laarif F Jonson H 2000lsquoPollen-based biome reconstruction for southernEurope and Africa 18000 yr BCrsquo Journal ofBiogeography Vol 27 621ndash34
Fairhead J and Leach M 1998 ReframingDeforestation global analyses and local realitiesstudies in West Africa London Routledge
Gueacutehi JI 1993 lsquoLa politique coloniale de protection dela nature en Cocircte drsquoIvoire (1900ndash1958)rsquo in JPouchepadass (ed) Colonisations et environnementBibliothegraveque drsquohistoire drsquooutre mer Nouvelle seacuterie Etudes13 Paris Soc fr drsquohistoire drsquooutre-mer 83ndash104
Guillaumet JL and Adjanohoun E 1971 lsquoLaveacutegeacutetation de la Cocircte drsquoIvoire Dans Le milieunaturel de la Cocircte drsquoIvoirersquo Meacutemoires ORSTOM No50 156ndash263
Hall JB and Swaine MD 1981 lsquoDistribution andecology of vascular plants in a tropical rain forestforest vegetation in Ghanarsquo Geobotany 1 TheHague Dr W Junk Publishers
Hawthorne W and Abu-Juam M 1995 ForestProtection in Ghana Gland IUCN
Hawthorne WD 1995 lsquoEcological profiles of theforest trees of Ghanarsquo Tropical Forests papers No 26Oxford Forestry Institute
Hawthorne WD 1996 lsquoHoles and the sums of partsin Ghanaian forest regeneration scale andsustainable usersquo Proceedings of the Royal SocietyEdinburgh Vol 104B 75ndash176
Jolly D Prentice C Bonnefille R Ballouche ABengo M Brenac P Buchet G Burney D CazetJ-P Cheddadi R Edorh T Elenga HElmoutaki S Guiot J Laarif F Lamb H LezineA-M Maley J Mbenza M Peyron O Reille MReynaud-Farrera I Riollet G Ritchie C RocheE Scott L Ssemmanda I Straka H Umer HVan Campo E Vilimumbalo S Vincens AWaller M 1998 lsquoBiome reconstruction from
pollen and plant macrofossil data for Africa and theArabian peninsula at 0 and 6000 yearsrsquo Journal ofBiogeography Vol 25 1007ndash27
Maley J 1996 lsquoThe African rain forest ndash maincharacteristics of changes in vegetation and climatefrom the Upper Cretaceous to the QuaternaryrsquoProceedings of the Royal Society Edinburgh Vol 104B31ndash73
Oldeman RAA 1990 Forests Elements of SilvologyHeidelberg Springer Verlag
Olesen HH 1994 lsquoTropical forest inventory usingAVHRR-HRPT and LAC data in West Africarsquo FinalReport on Contract No 5088-92-11 ED ISP CHGeneva UNEP-GRID
Parren MPE 1994 lsquoFrench and British colonialforest policies past and present implications forCocircte drsquoIvoire and Ghanarsquo Working Papers in AfricanStudies No 188 Boston African Studies CenterBoston University
Richards PW 1964 The Tropical Rain Forest Anecological study Cambridge Cambridge UniversityPress
Schwartz D 1992 lsquoAssegravechement climatique vers3000 BP et expansion Bantu en Afrique centraleatlantique quelques reacuteflexionsrsquo Bulletin de la SocieteGeacuteologique de France Vol 163 No 3 353ndash61
Van Rompaey RSAR 1993 lsquoForest gradients inWest Africa A spatial gradient analysisrsquo Doctoralthesis Department of Forestry AgriculturalUniversity Wageningen
Van Rompaey RSAR 2001 lsquoMegatransects inUpper Guinea how forest inventory data can beprocessed into a gradient maprsquo in Robbrechts Eand Degreef J (eds) Proceedings XVIth AETFATConference August 2000 Meise Belgium
White F 1983 lsquoThe vegetation of Africa a descriptivememoir to accompany the UNESCOAETFATUNSO vegetation map of Africarsquo Natural ResourcesResearch Paris UNESCO Vol XX
White F 1986 lsquoLa veacutegeacutetation de lrsquoAfrique meacutemoiresaccompagnant la carte de veacutegeacutetation de lrsquoAfriquersquo(UNESCOAETFATUNSO) ORSTOMUNESCORecherches sur les ressources naturelles Vol XX
White LJT 2001 lsquoForest-savanna dynamics and theorigins of lsquoMarantaceae Forestrsquo in central Gabonrsquo inB Weber LJT White A Vedder and L Naughton(eds) African Rain Forest Ecology and ConservationYale Yale University Press
Whitmore TC 1975 Tropical Rain Forests of the FarEast Oxford Clarendon Press
38
older analytics in forest ecology would haveexpected comprising very many seedlings manysaplings and fewer larger trees This makes theirregeneration difficult to predict and theirsustainable forest management hard to model Forexample one can compare the pioneer timber treesMilicia regia and excelsa (Figure 4) mainly found indrier forests with the shade-bearing tree Tarrietiautilis synonymous with Heritiera utilis (Figure 4)from the wet forests The light-demandingness ofspecies like Heritiera shifts from shade-bearing inyouth to growing in full light when mature Miliciatrees were always found growing in sunlitconditions in the Ghana timber inventoryregardless of age (Hawthorne 1995)
The light-demandingness of a species can also beread from the form of the size class distributionsteeply exponential for shade-bearers to flatlyexponential or irregular for pioneers (Figure 4)Tarrietia and Milicia have equal densities among thebig trees of the respectively wet and dry forestswhere they occur but in the small size class in wetevergreen forests Tarrietia is very abundant Miliciasaplings (5ndash30 cm diameter) and young trees(30ndash60 cm diameter) are ten times rarer in dry semi-deciduous forest and moreover they grow in sunlitplaces which are often more difficult to walkthrough These densities seem to be sufficient forboth species to survive in the forests where they livealthough Alder (1990) was unable to model a stablepopulation from the mortality and growth data from
Ghana that he processed An explanation may bethat successful regeneration only occurs within atime frame of several decades which is beyond themeasuring period of the Ghana Forest Service
5 Conclusion no uniform rainforest zone but two clearlydifferent systemsThe rain forest zone is clearly not a uniform cover ofundisturbed forest Rather present-day speciescomposition reflects both past disturbance regimesand gradients of water availability as they interact witha complex of other factors including soil types andland use While the outcomes of these interactingfactors are highly variable over space and time it ispossible to identify two poles within the forest zone
l Forests with continuous water availabilitythanks to a fairly constant climate andor waterretaining soils evergreen forests rich in rare andendemic species because there has been littleneed for the species to migrate and fewextinction events
l Forests with a long history of climaticdisturbance with irregular water availability anda climate with irregular dry spells semi-deciduousforests with few rare species and little endemism
These distinctions have important implications forrain forest conservation and management The
36
Figure 4 Size class distribution of the pioneer trees Milicia spp in dry semi-deciduous forest and the shade-bearer Tarrietia utilis in wet evergreen forest (Ghana national timber inventory Hawthorne 1995)
evergreen forests are of the highest conservationpriority and by fortuitous chance also contain fewertimber species of high economic value The semi-deciduous forests are of lower conservation priorityfor the sake of rare and endangered species althoughthe currently-undisturbed form of these forests hasbecome very rare and thus merits protection at anumber of places These forests have many timberspecies of high economic value and are thus ofgreatest value from a timber productivity perspective
51 Implications for conservationpriority setting
From Figure 2 it appears that the protected areasand forest reserves within the Upper Guinea regionare spread over the vegetation gradient in a ratheruneven way For example
l Sapo National Park is the only representative ofthe very wet evergreen forests of Liberia
l The Nimba Reserves in southern GuineaLiberia and Cocircte drsquoIvoire are the only protectedupland evergreen forests
l Taiuml Azagny and Banco National Parks (CocirctedrsquoIvoire) and Nini-Suhien National Park(Ghana) contain wet and transitional foresttypes while Bia and Kakum National Parks inGhana are transitional forests
l Marahoueacute National Park contains the driestsemi-deciduous forest at its boundary towoodland and secondary grassland This typeis also found in forest patches in ComoeacuteNational Park in north-east Cocircte drsquoIvoire
This overview therefore suggests that if forestconservation strategies are to represent the regionrsquos
forest types accurately Liberia should give protectedarea status to more of its very wet forests especiallyin the high rainfall zone (4000 mm rain annually) ineastern Liberia extending some 100 km inland fromthe coast Equally more upland evergreen orsubmontane forests in Liberia Guinea Cocircte drsquoIvoire(eg the Monts de Dan) and Ghana (eg the Atewarange Hawthorne and Abu-Juam 1995) deserveprotected area status Furthermore the driest forestsespecially in Ghana where they contain several localendemics might be seen to merit more conservationattention especially where they are under threatfrom fire timber and firewood logging
In short recent perspectives and research invegetation ecology make forests in West Africaharder to classify and the classes harder to map thanwas thought before Many tree species show survivalstrategies that allow them to deal with heavydisturbance whether of climatic or anthropogenicorigin When deciding on conservation andsustainable management options for these forestsevergreen and semi-deciduous forests show highlycontrasted opportunities while both representvariable and dynamic ecosystems which challengeearlier management models based on ideas of stablepopulations and regeneration patterns
Notes I should like to thank Melissa Leach and James
Fairhead for inviting me to the inspiring Brightonworkshop My research in West Africa has beenfunded by Wageningen University (1987ndash1993) andthe European Commission DG Dev ECOSYNProject (1996ndash2000) Many GIS layers have beenprovided by Conservation International Washingtonand WCMC Cambridge I also thank MPE Parrenfor useful comments on the manuscript and WDHawthorne for many discussions about these topicsThe author can be contacted onRenaatVanRompaeyULBacbe
37
ReferencesAlcamo J Leemans R and Kreileman E 1998
lsquoGlobal change scenarios of the 21st centuryrsquoResults from the IMAGE 21 Model KidlingtonPergamon
Alder D 1990 Ghafosim a projection system fornatural forest growth and yield in Ghana OxfordManas Systems Ltd
Aubreacuteville A 1938 lsquoLa forecirct coloniale Les forecircts delrsquoAfrique occidentale franccedilaisersquo Annales de lrsquoAcadeacutemiedes sciences coloniales tome IX Soc drsquoeacuteditionsgeacuteographiques maritimes et coloniales ParislrsquoAcadeacutemie des Sciences
Bongers F Poorter L Van Rompaey RSAR andParren MPE 1999 lsquoDistribution of twelve moistforest canopy tree species in Liberia and Cocircte
drsquoIvoire response curves to a climatic gradientrsquoJournal of Vegetation Science Vol 10 371ndash82
Dawkins HC 1958 The Management of NaturalTropical High-forest with Special Reference to UgandaInstitute Paper No 34 Imperial Forestry InstituteUniversity of Oxford Oxford
Elenga H Peyron O Bonnefille R Jolly DCheddadi R Guiot J Andrieu V Bottema SBuchet G De Beaulieu J-L Hamilton ACMaley J Marchant R Perez-Obiol R Reille MRiollet G Scott L Straka H Taylor D VanCampo E Vincens A Laarif F Jonson H 2000lsquoPollen-based biome reconstruction for southernEurope and Africa 18000 yr BCrsquo Journal ofBiogeography Vol 27 621ndash34
Fairhead J and Leach M 1998 ReframingDeforestation global analyses and local realitiesstudies in West Africa London Routledge
Gueacutehi JI 1993 lsquoLa politique coloniale de protection dela nature en Cocircte drsquoIvoire (1900ndash1958)rsquo in JPouchepadass (ed) Colonisations et environnementBibliothegraveque drsquohistoire drsquooutre mer Nouvelle seacuterie Etudes13 Paris Soc fr drsquohistoire drsquooutre-mer 83ndash104
Guillaumet JL and Adjanohoun E 1971 lsquoLaveacutegeacutetation de la Cocircte drsquoIvoire Dans Le milieunaturel de la Cocircte drsquoIvoirersquo Meacutemoires ORSTOM No50 156ndash263
Hall JB and Swaine MD 1981 lsquoDistribution andecology of vascular plants in a tropical rain forestforest vegetation in Ghanarsquo Geobotany 1 TheHague Dr W Junk Publishers
Hawthorne W and Abu-Juam M 1995 ForestProtection in Ghana Gland IUCN
Hawthorne WD 1995 lsquoEcological profiles of theforest trees of Ghanarsquo Tropical Forests papers No 26Oxford Forestry Institute
Hawthorne WD 1996 lsquoHoles and the sums of partsin Ghanaian forest regeneration scale andsustainable usersquo Proceedings of the Royal SocietyEdinburgh Vol 104B 75ndash176
Jolly D Prentice C Bonnefille R Ballouche ABengo M Brenac P Buchet G Burney D CazetJ-P Cheddadi R Edorh T Elenga HElmoutaki S Guiot J Laarif F Lamb H LezineA-M Maley J Mbenza M Peyron O Reille MReynaud-Farrera I Riollet G Ritchie C RocheE Scott L Ssemmanda I Straka H Umer HVan Campo E Vilimumbalo S Vincens AWaller M 1998 lsquoBiome reconstruction from
pollen and plant macrofossil data for Africa and theArabian peninsula at 0 and 6000 yearsrsquo Journal ofBiogeography Vol 25 1007ndash27
Maley J 1996 lsquoThe African rain forest ndash maincharacteristics of changes in vegetation and climatefrom the Upper Cretaceous to the QuaternaryrsquoProceedings of the Royal Society Edinburgh Vol 104B31ndash73
Oldeman RAA 1990 Forests Elements of SilvologyHeidelberg Springer Verlag
Olesen HH 1994 lsquoTropical forest inventory usingAVHRR-HRPT and LAC data in West Africarsquo FinalReport on Contract No 5088-92-11 ED ISP CHGeneva UNEP-GRID
Parren MPE 1994 lsquoFrench and British colonialforest policies past and present implications forCocircte drsquoIvoire and Ghanarsquo Working Papers in AfricanStudies No 188 Boston African Studies CenterBoston University
Richards PW 1964 The Tropical Rain Forest Anecological study Cambridge Cambridge UniversityPress
Schwartz D 1992 lsquoAssegravechement climatique vers3000 BP et expansion Bantu en Afrique centraleatlantique quelques reacuteflexionsrsquo Bulletin de la SocieteGeacuteologique de France Vol 163 No 3 353ndash61
Van Rompaey RSAR 1993 lsquoForest gradients inWest Africa A spatial gradient analysisrsquo Doctoralthesis Department of Forestry AgriculturalUniversity Wageningen
Van Rompaey RSAR 2001 lsquoMegatransects inUpper Guinea how forest inventory data can beprocessed into a gradient maprsquo in Robbrechts Eand Degreef J (eds) Proceedings XVIth AETFATConference August 2000 Meise Belgium
White F 1983 lsquoThe vegetation of Africa a descriptivememoir to accompany the UNESCOAETFATUNSO vegetation map of Africarsquo Natural ResourcesResearch Paris UNESCO Vol XX
White F 1986 lsquoLa veacutegeacutetation de lrsquoAfrique meacutemoiresaccompagnant la carte de veacutegeacutetation de lrsquoAfriquersquo(UNESCOAETFATUNSO) ORSTOMUNESCORecherches sur les ressources naturelles Vol XX
White LJT 2001 lsquoForest-savanna dynamics and theorigins of lsquoMarantaceae Forestrsquo in central Gabonrsquo inB Weber LJT White A Vedder and L Naughton(eds) African Rain Forest Ecology and ConservationYale Yale University Press
Whitmore TC 1975 Tropical Rain Forests of the FarEast Oxford Clarendon Press
38
evergreen forests are of the highest conservationpriority and by fortuitous chance also contain fewertimber species of high economic value The semi-deciduous forests are of lower conservation priorityfor the sake of rare and endangered species althoughthe currently-undisturbed form of these forests hasbecome very rare and thus merits protection at anumber of places These forests have many timberspecies of high economic value and are thus ofgreatest value from a timber productivity perspective
51 Implications for conservationpriority setting
From Figure 2 it appears that the protected areasand forest reserves within the Upper Guinea regionare spread over the vegetation gradient in a ratheruneven way For example
l Sapo National Park is the only representative ofthe very wet evergreen forests of Liberia
l The Nimba Reserves in southern GuineaLiberia and Cocircte drsquoIvoire are the only protectedupland evergreen forests
l Taiuml Azagny and Banco National Parks (CocirctedrsquoIvoire) and Nini-Suhien National Park(Ghana) contain wet and transitional foresttypes while Bia and Kakum National Parks inGhana are transitional forests
l Marahoueacute National Park contains the driestsemi-deciduous forest at its boundary towoodland and secondary grassland This typeis also found in forest patches in ComoeacuteNational Park in north-east Cocircte drsquoIvoire
This overview therefore suggests that if forestconservation strategies are to represent the regionrsquos
forest types accurately Liberia should give protectedarea status to more of its very wet forests especiallyin the high rainfall zone (4000 mm rain annually) ineastern Liberia extending some 100 km inland fromthe coast Equally more upland evergreen orsubmontane forests in Liberia Guinea Cocircte drsquoIvoire(eg the Monts de Dan) and Ghana (eg the Atewarange Hawthorne and Abu-Juam 1995) deserveprotected area status Furthermore the driest forestsespecially in Ghana where they contain several localendemics might be seen to merit more conservationattention especially where they are under threatfrom fire timber and firewood logging
In short recent perspectives and research invegetation ecology make forests in West Africaharder to classify and the classes harder to map thanwas thought before Many tree species show survivalstrategies that allow them to deal with heavydisturbance whether of climatic or anthropogenicorigin When deciding on conservation andsustainable management options for these forestsevergreen and semi-deciduous forests show highlycontrasted opportunities while both representvariable and dynamic ecosystems which challengeearlier management models based on ideas of stablepopulations and regeneration patterns
Notes I should like to thank Melissa Leach and James
Fairhead for inviting me to the inspiring Brightonworkshop My research in West Africa has beenfunded by Wageningen University (1987ndash1993) andthe European Commission DG Dev ECOSYNProject (1996ndash2000) Many GIS layers have beenprovided by Conservation International Washingtonand WCMC Cambridge I also thank MPE Parrenfor useful comments on the manuscript and WDHawthorne for many discussions about these topicsThe author can be contacted onRenaatVanRompaeyULBacbe
37
ReferencesAlcamo J Leemans R and Kreileman E 1998
lsquoGlobal change scenarios of the 21st centuryrsquoResults from the IMAGE 21 Model KidlingtonPergamon
Alder D 1990 Ghafosim a projection system fornatural forest growth and yield in Ghana OxfordManas Systems Ltd
Aubreacuteville A 1938 lsquoLa forecirct coloniale Les forecircts delrsquoAfrique occidentale franccedilaisersquo Annales de lrsquoAcadeacutemiedes sciences coloniales tome IX Soc drsquoeacuteditionsgeacuteographiques maritimes et coloniales ParislrsquoAcadeacutemie des Sciences
Bongers F Poorter L Van Rompaey RSAR andParren MPE 1999 lsquoDistribution of twelve moistforest canopy tree species in Liberia and Cocircte
drsquoIvoire response curves to a climatic gradientrsquoJournal of Vegetation Science Vol 10 371ndash82
Dawkins HC 1958 The Management of NaturalTropical High-forest with Special Reference to UgandaInstitute Paper No 34 Imperial Forestry InstituteUniversity of Oxford Oxford
Elenga H Peyron O Bonnefille R Jolly DCheddadi R Guiot J Andrieu V Bottema SBuchet G De Beaulieu J-L Hamilton ACMaley J Marchant R Perez-Obiol R Reille MRiollet G Scott L Straka H Taylor D VanCampo E Vincens A Laarif F Jonson H 2000lsquoPollen-based biome reconstruction for southernEurope and Africa 18000 yr BCrsquo Journal ofBiogeography Vol 27 621ndash34
Fairhead J and Leach M 1998 ReframingDeforestation global analyses and local realitiesstudies in West Africa London Routledge
Gueacutehi JI 1993 lsquoLa politique coloniale de protection dela nature en Cocircte drsquoIvoire (1900ndash1958)rsquo in JPouchepadass (ed) Colonisations et environnementBibliothegraveque drsquohistoire drsquooutre mer Nouvelle seacuterie Etudes13 Paris Soc fr drsquohistoire drsquooutre-mer 83ndash104
Guillaumet JL and Adjanohoun E 1971 lsquoLaveacutegeacutetation de la Cocircte drsquoIvoire Dans Le milieunaturel de la Cocircte drsquoIvoirersquo Meacutemoires ORSTOM No50 156ndash263
Hall JB and Swaine MD 1981 lsquoDistribution andecology of vascular plants in a tropical rain forestforest vegetation in Ghanarsquo Geobotany 1 TheHague Dr W Junk Publishers
Hawthorne W and Abu-Juam M 1995 ForestProtection in Ghana Gland IUCN
Hawthorne WD 1995 lsquoEcological profiles of theforest trees of Ghanarsquo Tropical Forests papers No 26Oxford Forestry Institute
Hawthorne WD 1996 lsquoHoles and the sums of partsin Ghanaian forest regeneration scale andsustainable usersquo Proceedings of the Royal SocietyEdinburgh Vol 104B 75ndash176
Jolly D Prentice C Bonnefille R Ballouche ABengo M Brenac P Buchet G Burney D CazetJ-P Cheddadi R Edorh T Elenga HElmoutaki S Guiot J Laarif F Lamb H LezineA-M Maley J Mbenza M Peyron O Reille MReynaud-Farrera I Riollet G Ritchie C RocheE Scott L Ssemmanda I Straka H Umer HVan Campo E Vilimumbalo S Vincens AWaller M 1998 lsquoBiome reconstruction from
pollen and plant macrofossil data for Africa and theArabian peninsula at 0 and 6000 yearsrsquo Journal ofBiogeography Vol 25 1007ndash27
Maley J 1996 lsquoThe African rain forest ndash maincharacteristics of changes in vegetation and climatefrom the Upper Cretaceous to the QuaternaryrsquoProceedings of the Royal Society Edinburgh Vol 104B31ndash73
Oldeman RAA 1990 Forests Elements of SilvologyHeidelberg Springer Verlag
Olesen HH 1994 lsquoTropical forest inventory usingAVHRR-HRPT and LAC data in West Africarsquo FinalReport on Contract No 5088-92-11 ED ISP CHGeneva UNEP-GRID
Parren MPE 1994 lsquoFrench and British colonialforest policies past and present implications forCocircte drsquoIvoire and Ghanarsquo Working Papers in AfricanStudies No 188 Boston African Studies CenterBoston University
Richards PW 1964 The Tropical Rain Forest Anecological study Cambridge Cambridge UniversityPress
Schwartz D 1992 lsquoAssegravechement climatique vers3000 BP et expansion Bantu en Afrique centraleatlantique quelques reacuteflexionsrsquo Bulletin de la SocieteGeacuteologique de France Vol 163 No 3 353ndash61
Van Rompaey RSAR 1993 lsquoForest gradients inWest Africa A spatial gradient analysisrsquo Doctoralthesis Department of Forestry AgriculturalUniversity Wageningen
Van Rompaey RSAR 2001 lsquoMegatransects inUpper Guinea how forest inventory data can beprocessed into a gradient maprsquo in Robbrechts Eand Degreef J (eds) Proceedings XVIth AETFATConference August 2000 Meise Belgium
White F 1983 lsquoThe vegetation of Africa a descriptivememoir to accompany the UNESCOAETFATUNSO vegetation map of Africarsquo Natural ResourcesResearch Paris UNESCO Vol XX
White F 1986 lsquoLa veacutegeacutetation de lrsquoAfrique meacutemoiresaccompagnant la carte de veacutegeacutetation de lrsquoAfriquersquo(UNESCOAETFATUNSO) ORSTOMUNESCORecherches sur les ressources naturelles Vol XX
White LJT 2001 lsquoForest-savanna dynamics and theorigins of lsquoMarantaceae Forestrsquo in central Gabonrsquo inB Weber LJT White A Vedder and L Naughton(eds) African Rain Forest Ecology and ConservationYale Yale University Press
Whitmore TC 1975 Tropical Rain Forests of the FarEast Oxford Clarendon Press
38
drsquoIvoire response curves to a climatic gradientrsquoJournal of Vegetation Science Vol 10 371ndash82
Dawkins HC 1958 The Management of NaturalTropical High-forest with Special Reference to UgandaInstitute Paper No 34 Imperial Forestry InstituteUniversity of Oxford Oxford
Elenga H Peyron O Bonnefille R Jolly DCheddadi R Guiot J Andrieu V Bottema SBuchet G De Beaulieu J-L Hamilton ACMaley J Marchant R Perez-Obiol R Reille MRiollet G Scott L Straka H Taylor D VanCampo E Vincens A Laarif F Jonson H 2000lsquoPollen-based biome reconstruction for southernEurope and Africa 18000 yr BCrsquo Journal ofBiogeography Vol 27 621ndash34
Fairhead J and Leach M 1998 ReframingDeforestation global analyses and local realitiesstudies in West Africa London Routledge
Gueacutehi JI 1993 lsquoLa politique coloniale de protection dela nature en Cocircte drsquoIvoire (1900ndash1958)rsquo in JPouchepadass (ed) Colonisations et environnementBibliothegraveque drsquohistoire drsquooutre mer Nouvelle seacuterie Etudes13 Paris Soc fr drsquohistoire drsquooutre-mer 83ndash104
Guillaumet JL and Adjanohoun E 1971 lsquoLaveacutegeacutetation de la Cocircte drsquoIvoire Dans Le milieunaturel de la Cocircte drsquoIvoirersquo Meacutemoires ORSTOM No50 156ndash263
Hall JB and Swaine MD 1981 lsquoDistribution andecology of vascular plants in a tropical rain forestforest vegetation in Ghanarsquo Geobotany 1 TheHague Dr W Junk Publishers
Hawthorne W and Abu-Juam M 1995 ForestProtection in Ghana Gland IUCN
Hawthorne WD 1995 lsquoEcological profiles of theforest trees of Ghanarsquo Tropical Forests papers No 26Oxford Forestry Institute
Hawthorne WD 1996 lsquoHoles and the sums of partsin Ghanaian forest regeneration scale andsustainable usersquo Proceedings of the Royal SocietyEdinburgh Vol 104B 75ndash176
Jolly D Prentice C Bonnefille R Ballouche ABengo M Brenac P Buchet G Burney D CazetJ-P Cheddadi R Edorh T Elenga HElmoutaki S Guiot J Laarif F Lamb H LezineA-M Maley J Mbenza M Peyron O Reille MReynaud-Farrera I Riollet G Ritchie C RocheE Scott L Ssemmanda I Straka H Umer HVan Campo E Vilimumbalo S Vincens AWaller M 1998 lsquoBiome reconstruction from
pollen and plant macrofossil data for Africa and theArabian peninsula at 0 and 6000 yearsrsquo Journal ofBiogeography Vol 25 1007ndash27
Maley J 1996 lsquoThe African rain forest ndash maincharacteristics of changes in vegetation and climatefrom the Upper Cretaceous to the QuaternaryrsquoProceedings of the Royal Society Edinburgh Vol 104B31ndash73
Oldeman RAA 1990 Forests Elements of SilvologyHeidelberg Springer Verlag
Olesen HH 1994 lsquoTropical forest inventory usingAVHRR-HRPT and LAC data in West Africarsquo FinalReport on Contract No 5088-92-11 ED ISP CHGeneva UNEP-GRID
Parren MPE 1994 lsquoFrench and British colonialforest policies past and present implications forCocircte drsquoIvoire and Ghanarsquo Working Papers in AfricanStudies No 188 Boston African Studies CenterBoston University
Richards PW 1964 The Tropical Rain Forest Anecological study Cambridge Cambridge UniversityPress
Schwartz D 1992 lsquoAssegravechement climatique vers3000 BP et expansion Bantu en Afrique centraleatlantique quelques reacuteflexionsrsquo Bulletin de la SocieteGeacuteologique de France Vol 163 No 3 353ndash61
Van Rompaey RSAR 1993 lsquoForest gradients inWest Africa A spatial gradient analysisrsquo Doctoralthesis Department of Forestry AgriculturalUniversity Wageningen
Van Rompaey RSAR 2001 lsquoMegatransects inUpper Guinea how forest inventory data can beprocessed into a gradient maprsquo in Robbrechts Eand Degreef J (eds) Proceedings XVIth AETFATConference August 2000 Meise Belgium
White F 1983 lsquoThe vegetation of Africa a descriptivememoir to accompany the UNESCOAETFATUNSO vegetation map of Africarsquo Natural ResourcesResearch Paris UNESCO Vol XX
White F 1986 lsquoLa veacutegeacutetation de lrsquoAfrique meacutemoiresaccompagnant la carte de veacutegeacutetation de lrsquoAfriquersquo(UNESCOAETFATUNSO) ORSTOMUNESCORecherches sur les ressources naturelles Vol XX
White LJT 2001 lsquoForest-savanna dynamics and theorigins of lsquoMarantaceae Forestrsquo in central Gabonrsquo inB Weber LJT White A Vedder and L Naughton(eds) African Rain Forest Ecology and ConservationYale Yale University Press
Whitmore TC 1975 Tropical Rain Forests of the FarEast Oxford Clarendon Press
